Fix filter generation

Filters were not created correctly. They did not check if we were given a short
tag or project. And they did not generate the correct tag and filter name once
finding one. This fixes both issues so we can do filter correctly.
Fix bug in edit_proj

That function listed the tags, and not the current project. This commit fixes
that so we now show the current project(s), not tags.
Add modify action

Modify allows someone direct access to taskwarrior's input. This may be useful
for detailed changes, or ones outside the simple things I have provided short
cuts for.
Add variables for abbreviations

I shorten tag and projects by adding @ and $, so I've added variables to
configure that choice. Hopefully that is useful later.
Add syntax group name
Add some utility functions
Stub some doc stuff