Doc fixes (thanks to Rafał Babinicz)
Version bumped also in docs
fix build on old versions of ghc by qualifying import to avoid conflict
A hint for spotify users
cabal file updates for 0.21
CoreCommon: Try several paths in checkedDataRetrieval
CoreTemp: Add alternative path for linux 3.15

Since v3.15-rc1, coretemp temperatures are elsewhere, see
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=d72d19c26c417d514787ae85b197af34de286c0a
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=bab2243ce1897865e31ea6d59b0478391f51812b
Credits for Tomas
Fix: referencing the correct header in StatFs
Accepting "unknown" as network device state

Cf. discussion of issue #98