add more stolen syntax to the user guide

[maeder]

language extensions:

- Bang Patterns disallow an infix funlhs for "!"

- Magic Hash disallows sections like "(3#)" and infix terms like "3# 1" without a space before # (for a user-defined operator "#" or "##")

[maeder]

I think, -XBangPatterns should be mentioned under http://www.haskell.org/ghc/docs/7.4.1/html/users_guide/syntax-extns.html#syntax-stolen

The problems for user-defined infix-operators starting with "#" (namely requiring a white space on the left) should be described under http://www.haskell.org/ghc/docs/7.4.1/html/users_guide/syntax-extns.html#magic-hash

(http://www.haskell.org/ghc/docs/7.4.1/html/users_guide/bang-patterns.html mentions later:

Is this a definition of the infix function "(!)", or of the "f" with a bang pattern? GHC resolves this ambiguity in favour of the latter. If you want to define (!) with bang-patterns enabled, you have to do so using prefix notation: 

)