First Pass at Multiline Strings

[floralvikings]

My attempt at implementing multi-line strings

This is still in a fairly rough state:

• Only "folded" (using >) strings are implemented
• Code could use some review and possibly some cleanup

However, if this approach is acceptable, I can add support and an equivalent set of tests for "literal" (using |) strings as well.

Please let me know if there are test cases I'm missing! Multiline strings in YAML are way more complicated than I initially realized so I'm sure there's something I haven't thought of.

[floralvikings]

I went ahead and added tests and support for literal style strings; even if the implementation isn't up to snuff, the tests should still be useful

[floralvikings]

@Him188 I've updated the PR in 7f017cf, I've extracted some duplicate code into functions where possible and left comments detailing the differences between the functions that couldn't be easily combined