Previously we'd get an error if the first lines in the mappings file
were blank or comments.

This broke recently I think. You can no longer have a mappings file that
starts with blank lines or comment lines.

Removing the empty and blank handler in `definitions()` fixes the tests
added by this commit but fails these:

    parser::tests::map_group_empty_input_does_not_fail
    parser::tests::map_group_skipped_input_outputs_default_map_group

Using this diff:

    diff --git a/src/parser.rs b/src/parser.rs
    index 3f3d7b9..d18b56a 100644
    --- a/src/parser.rs
    +++ b/src/parser.rs
    @@ -629,11 +629,11 @@ where
         I: Stream<Item = char>,
         I::Error: ParseError<I::Item, I::Range, I::Position>,
     {
    -    or(
    -        (
    -            blank(),
    -            eof(),
    -        ).map(|_| MapGroup::default()),
    +    // or(
    +    //     (
    +    //         blank(),
    +    //         eof(),
    +    //     ).map(|_| MapGroup::default()),
             (
                 definitions(),
                 eof(),
    @@ -661,8 +661,8 @@ where
                 }

                 map_group
    -        }),
    -    )
    +        })
    +    // )
     }

     fn comment<I>() -> impl Parser<Input = I>

Need to figure out some way to get both sets of tests to pass.

Don't need these programs any more, so the build recipes for them don't
really make sense to keep.

Also remove the `clean` target since it only relates to `includer` and
`moder`.

Ready for a stable release.

* Release targets for 'dome_key_event_source_simulator'
* Add `release` target

Remove the TODO key and use a real one instead. A description of the
program.