Improve the parser error messages

[nikita-volkov]

Attoparsec's messages seem to be anything but useful. I mean I get

    Parser failure: Failed reading: satisfy. Contexts: ["exp","'('"].

for almost any syntactical mistake. I guess unless there'll be major changes involving integration with "haskell-src-exts", we'll have to switch to Parsec.

Suggestions?

[nikita-volkov]

Just a heads up. The preprocessor reimplementation addresses this.

[rabipelais]

Also, the current parser (I don't know about the new implementation) chokes up with infix operators, like <$> or !*! (from Linear) when used in record expressions, for example:
x = [r| {matrix = mat1 !*! mat2, wrappedNumber = fromIntegral <$> stuff} |]

(I does work if I let-bind the sub expressions and then assign them, i.e. [r| {matrix = mat',....}|] where mat' = mat1 !*! mat2...)

[nikita-volkov]

@rabipelais It's just the lack of the support for this part of syntax in the current parser implementation. The preprocessor version will support all of the Haskell syntax.