Make ={...} syntax support optional

[rowanseymour]

This PR punts on the question of deprecating ={...} for now, and just makes it optional using the HAMLPY_DJANGO_INLINE_STYLE setting.

I still think deprecation is the way to go, especially once we add support for .(attr=val) syntax which introduces yet another meaning for =. I just want more time to think through the path to becoming more HAML and less HAMLPY. It bothers me that we'll be supporting three different syntaxes for attributes (.{attr:val}, .{attr=>val} and .(attr=val)) but dropping support for syntax that people are using is always tricky.

Addresses #16. @Psycojoker please review

[coveralls]

Coverage decreased (-0.07%) to 80.413% when pulling bb5aaf4 on optional_sub_syntax into bf64dde on master.

[Psycojoker]

It would be great to find a way to throw a depreciation warning if we find that the old syntax is still used instead of disabling it by default and breaking on a "pip -U".

I don't know if it's a lot of work :/

[rowanseymour]

@Psycojoker agreed but this PR doesn't disable it by default - this PR is completely backwards compatible

[coveralls]

Coverage decreased (-0.05%) to 79.122% when pulling a3a20fa on optional_sub_syntax into 038d993 on master.

[Psycojoker]

Oh, my bad, shouldn't review tired after work, sorry :/

[rowanseymour]

Np. Did you actually get a chance to look at the code? Would really love to get this merged as we need this to use the latest django-hamlpy with our main project.

[rowanseymour]

@Psycojoker bump. I don't like to pester but this PR has been open almost two weeks and we need it

[coveralls]

Coverage decreased (-0.06%) to 79.333% when pulling da81981 on optional_sub_syntax into 05be260 on master.

[coveralls]

Coverage decreased (-0.005%) to 92.031% when pulling 22dfa7d on optional_sub_syntax into cc7695b on master.