Make using builtin commands / metas more user-friendly.

[benoit-pierre]

Add user-friendly names for builtin metas (e.g. {:retro_currency:$c}), and ignore case when processing builtins commands / metas (so {PloveR:toggle} or {:mode:Camel} will work as expected).

Fix #688 and #870.

[morinted]

What is the behavior of {:attach}? Would it be like {:attach:^ing}, with {:attach:word} having no effect?

[morinted]

We may also consider affix over attach

[benoit-pierre]

What is the behavior of {:attach}? Would it be like {:attach:^ing}, with {:attach:word} having no effect?

    def test_meta_attach_4(self):
        r'''
        'TEFT': 'test',
        'AT': '{:attach:attach}',

        TEFT/AT  ' test attach'
        '''

[benoit-pierre]

We may also consider affix over attach

Sure, do if you think it's clearer, do you want me to change it?

[benoit-pierre]

Regarding the behavior of {:attach:attach}, we could change it so it's equivalent to {:attach:^attach^}.

[morinted]

Regarding the behavior of {:attach:attach}, we could change it so it's equivalent to {:attach:^attach^}.

I like both of these suggestions if you want to add the changes to this PR

[benoit-pierre]

@morinted: I changed the default for {:attach:attach}. Just to be clear, you want also the meta to be renamed to affix?

[morinted]

Thanks for the changes. I think "affix" is more technically correct, but "attach" will probably be easier to understand for users. Let's merge as-is.