trailing spaces not handled in sexprs

[abiduzz420]

When writing s-expressions having trailing spaces inside parens, the interpreter gives parse error.

(+ 2 3   ) 
(   define x 2)

Changes are to be made at https://github.com/abiduzz420/haskeme/blob/master/src/Haskeme/Parser.hs#L84

This issue was tried earlier but did not make a lot of progress instead injected new errors into defining functions etc

1. 40b41b4
2. befff57