Add syntax highlighting for features inside strings

[qix]

Problem

Features inside strings are not highlighted

Solution

Add custom theme with color, and tokenize it

Result

Features are now highlighted

[coveralls]

Pull Request Test Coverage Report for Build 3695539978

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 61.091%

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Totals
Change from base Build 3689647636:	0.0%
Covered Lines:	15799
Relevant Lines:	24113

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💛 - Coveralls