Eta reduce zipWith* functions

It's done to allow inlining even if function application is not fully
saturated. It's important because simple stylistic change could change
performance by order of magnitudes

Fixes #4
Silence error about missing methods
Update .travis.yml to include GHC 7.8.2
Merge pull request #7 from Shimuuar/eta-reduce

Split argument lists of zipWith* for better inlining and stub methods for Num Size instance
Add LANGUAGE extensions for inferred signatures.

Some of the inferred signatures required LANGUAGE extensions that
were not enabled. Since now GHC checks that we have to explicitly
list required extensions.

(cherry picked from commit a6049abce040713e9a5f175887cf70d12b9057c6)

This should fix #25

Conflicts:
	Data/Vector/Generic/Mutable.hs
	Data/Vector/Mutable.hs
Move CPP pragmas outside {-# RULES #-}, re #21.