7 lexing implementation

[mraasvel]

Add support for:

• Backslash
• Single quotes
• Double quotes
• Expansions (recursive lexing)
• Backticks
• IoNumber

Testing:

• Parameterized tests for lexer
• Add printing option and sections

[mraasvel]

To add:

• IO_NUMBER
• Use Token instead of Word token type in the lexer (#24)
• Backtick, command substitution, parameter expansion, and arithmetic expansion

[mraasvel]

Added custom prompt based on lexer state, IoNumber, Type::Token, backticks and recursive lexing support. Still left to do:

• Newline handling inside of a () parenthesis operator state and maybe also the braces state {}, e.g. (\n) {\n}. The standard doesn't mention these, but bash handles them so we might want to support that.
• Make a graph for all the state transitions