v0.1.0

Additions:

* Passextract can now be invoked as a standalone program instead of
  requiring input to be passed to it through STDIN. It will take a file
  argument in exactly the same way as `pass show`. When run in this way,
  the program will call `pass show` with the given argument and display
  the result in the Passextract interactive interface. It is still
  possible to use the program with STDIN.
* A Bash completion script is added that enables tab completion and
  functions in the same way as `pass show`.
* A license, README, and demo screencast are added.