Add support for floats

[gregorybchris]

• Add FloatLit
• Update Lexer to support tokenizing numbers with decimal parts
• Add Float object
• Update Parser to parse FloatLit into Float
• Update arithmetic binops to work for both Int and Float
• Add matching support for Float objects
• Add serialize/bencode support for Float objects

[tekknolagi]

please "squash and merge" using github ui