Integer literal frontend

[AStenbaek]

Resolves #56

Tasks:

• Updated the lexer to support expanded notation for integer literals. The implementation is simple, relying on the the Haskell Numeric library.
• Added tests all mirror the behavior of OCaml.
• Currently, 0b117 gets parsed as 3, leaving 7 as a separate number. In this case, the runtime breaks as it tries to 3(7). Instead, this should be an error at compile time.

[aslanix]

This needs to fix the missing todos, and add negative tests. For example, 0x________A is rejected by the OCaml.

[AStenbaek]

The feature should be implemented now.
I do not know why two multi-node tests failed in the GitHub action, but all tests passes on my machine.