Normalize registered function names

Since they also get called in the normalized form
(underscores are replaced with hyphens) function
names should also be normalized on initialization.
Updates sass2scss module to latest version
Merge pull request #433 from mgreter/function_name_normalize

Normalize registered function names
normalize underscores for iteration variables in @each and @for blocks
Merge branch 'master' into interchangeable_hyphens_underscores
Merge pull request #436 from wonja/interchangeable_hyphens_underscores

Interchangeable hyphens underscores #435