Please add section on (doc)strings

[0joshuaolson1]

• which version/flavor of markdown
• ~Does Pony have single-quoted char(acter)s? Unicode?~
• line breaks always interpreted literally
• ~escapable characters~

Literal Unicode (rather than numeric codes) support would affect valid encodings for pony source files.

[mfelsche]

points 2 to 4 are already covered by the literals section. point 1 still needs to be covered.

[rhagenson]

Represents one part of addressing #320