I recently tried installing the program via Homebrew on a machine that
didn't have 'libgit2' installed. The Homebrew formula installs pre-built
binaries. Running the binaries gave me an error saying that the
'libgit2' dynamic library couldn't be found.

Change the build configuration to build a "static" binary. It still
links to system dylibs, but I've removed all links to Homebrew dylibs.
These were:

* libgit2
* openssl

Removed the 'openssl' link by adding the 'vendored-openssl' feature to
the 'git2' dependency.

In order to remove the 'libgit2' link, I had to do some more finagling.
Accomplished this by setting an empty `PKG_CONFIG_LIBDIR` when building.
While 'git2' doesn't have a Cargo feature to disable dynamic linking, we
can force static linking by preventing `pkg-config` from finding the
Homebrew-installed 'libgit2'. The 'libgit2-sys' crate's build script
first checks for the library using `pkg-config`, and builds it
statically if it doesn't exist:

https://github.com/rust-lang/git2-rs/blob/43d583fd8b50fad0cfe0bbc334059ce965b6f3fc/libgit2-sys/build.rs#L15-L17

With these changes, the above packages will now be statically linked
with the program's binaries.

Upgrade 'git2' to the latest version (0.13.11) since we're changing its
build configuration.

Before:

    $ otool -L target/release/git-sug*
    target/release/git-sugapply:
      /System/Library/Frameworks/Security.framework/Versions/A/Security (compatibility version 1.0.0, current version 57740.60.18)
      /usr/local/opt/libgit2/lib/libgit2.1.0.dylib (compatibility version 1.0.0, current version 1.0.1)
      /usr/local/opt/openssl@1.1/lib/libssl.1.1.dylib (compatibility version 1.1.0, current version 1.1.0)
      /usr/local/opt/openssl@1.1/lib/libcrypto.1.1.dylib (compatibility version 1.1.0, current version 1.1.0)
      /usr/lib/libz.1.dylib (compatibility version 1.0.0, current version 1.2.8)
      /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1238.60.2)
      /usr/lib/libresolv.9.dylib (compatibility version 1.0.0, current version 1.0.0)
    target/release/git-sugapply.d: is not an object file
    target/release/git-sugdiff:
      /System/Library/Frameworks/Security.framework/Versions/A/Security (compatibility version 1.0.0, current version 57740.60.18)
      /usr/local/opt/libgit2/lib/libgit2.1.0.dylib (compatibility version 1.0.0, current version 1.0.1)
      /usr/local/opt/openssl@1.1/lib/libssl.1.1.dylib (compatibility version 1.1.0, current version 1.1.0)
      /usr/local/opt/openssl@1.1/lib/libcrypto.1.1.dylib (compatibility version 1.1.0, current version 1.1.0)
      /usr/lib/libz.1.dylib (compatibility version 1.0.0, current version 1.2.8)
      /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1238.60.2)
      /usr/lib/libresolv.9.dylib (compatibility version 1.0.0, current version 1.0.0)
    target/release/git-sugdiff.d: is not an object file

After:

    $ otool -L target/release/git-sug*
    target/release/git-sugapply:
      /System/Library/Frameworks/Security.framework/Versions/A/Security (compatibility version 1.0.0, current version 57740.60.18)
      /usr/lib/libiconv.2.dylib (compatibility version 7.0.0, current version 7.0.0)
      /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation (compatibility version 150.0.0, current version 1349.8.0)
      /usr/lib/libz.1.dylib (compatibility version 1.0.0, current version 1.2.8)
      /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1238.60.2)
      /usr/lib/libresolv.9.dylib (compatibility version 1.0.0, current version 1.0.0)
    target/release/git-sugapply.d: is not an object file
    target/release/git-sugdiff:
      /System/Library/Frameworks/Security.framework/Versions/A/Security (compatibility version 1.0.0, current version 57740.60.18)
      /usr/lib/libiconv.2.dylib (compatibility version 7.0.0, current version 7.0.0)
      /System/Library/Frameworks/CoreFoundation.framework/Versions/A/CoreFoundation (compatibility version 150.0.0, current version 1349.8.0)
      /usr/lib/libz.1.dylib (compatibility version 1.0.0, current version 1.2.8)
      /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1238.60.2)
      /usr/lib/libresolv.9.dylib (compatibility version 1.0.0, current version 1.0.0)
    target/release/git-sugdiff.d: is not an object file

Now that I'm using the name "git-suggestion" in a few places, and from a
user perspective, it's more Git-oriented than GitHub-oriented, I think
the crate should be renamed to reflect that.

Not sure if I should be emphasising this more.

Make the list easier to scan by ordering it alphabetically. Also, I
noticed there were two `-p` flags listed, so ran the flags through
`uniq`.

Now that I added `program_args`, reading this back over I realised
`found_args` didn't convey enough information about what it contains.

Didn't look closely enough in d9b8838a5d99e643a751d042047644cfa4a9a032,
but we now have the exact same handling for key-value options and flags.