Revert "Reorganized files, language code in src/lang parsing in src/parsing"

This reverts commit 69173c811243aa4d35f6f8633c1ebd59d4b4dbbf.

Decided that files should not be reorganized!
Merge branch 'master' of https://github.com/shermpay/smallisp
Merge branch 'master' of https://github.com/shermpay/smallisp
Lexer that lexes numbers