More functionality

[ghost]

Tried to tidy up the README abit to reflect upon the changes made.

Erlang specific:

• Context is now a map (old dict still supported but will be converted to a map)
• Possibility to use binaries
• Fix failing tests due to regression with meck

Mustache:

• Dot-notation for nested maps
• Dot-notation for this element in list sections ({{.}})
• Simple lambda functions
• Ability to change the set delimiters

[ghost]

Maybe it was stupid to do the changes to using maps in the same PR. I'll see if I can split it up if I get time.