Prevent adding an empty note

Often user might accidentally add an empty note. Implemented a check so
that empty notes can't be added.

Signed-off-by: Niko Rosvall <niko@ideabyte.net>
Usage updates

Signed-off-by: Niko Rosvall <niko@ideabyte.net>
Add support for setting memo file path via an environment variable

Memo now supports MEMO_PATH environment variable. It's possible to set
memo file path using MEMO_PATH env variable.
For example: export MEMO_PATH=/some/path/to/file

Signed-off-by: Niko Rosvall <niko@ideabyte.net>
Increase version number and remove whitespace

Signed-off-by: Niko Rosvall <niko@ideabyte.net>
Update help

Signed-off-by: Niko Rosvall <niko@ideabyte.net>
Add environment variable documentation

Signed-off-by: Niko Rosvall <niko@ideabyte.net>