Add assertEquals function to compare two String bindings.

- I've added an assertEquals function to the cue text fixture in order for the
unit tests to easily compare two string bindings together. The assertEquals
fucntion calls Google Test's ASSERT_STREQ macro and passes in the String
binding's array casted to const char *.
- Change rest of unit tests to use assertEquals( String, String ) func.
Add assertEquals that takes a const char * and a string.

I've added an assertEquals that takes a const char * and a string. In this way
we can pass in the expected value as just a string literal and actual value as
a String binding.
Merge pull request #170 from RickEyre/issue-101

Add assertEquals function to compare two String bindings.