Make all possible operators allowed in string interpolation

Not sure why I haven't done it earlier...

fixes #49
Treat default clause for case statement as a whole with colon in bnf
grammar

This commit removes ambiguity from case statement grammars, it seems default
lexer parses this statement as a whole. Also improved tests for case
statements to actually catch related bug.

fixes #48
Merge pull request #50 from ap4y/string_interpolation_all_op

Make all possible operators allowed in string interpolation
Merge pull request #51 from ap4y/fix_default_case_indentation

Treat default clause for case statement as a whole with colon in bnf grammar
Apply DECSPEC token class only for functions
Apply swift-indent-offset to multi-line class definitions
Use semantic smie function instead of regex for multi-line dot
expression indentation
Merge pull request #52 from ap4y/fix_47

Fix 47
Merge pull request #53 from ap4y/improve_smie_dot_exp_rule

Use semantic smie function instead of regex for multi-line dot expression indentation