Add support for build-depends field

Now each dependency is explicitely printed out and for the formatting
options 'ghc' and 'hdevtools' an addtional '-hide-all-packages' is
printed out.

This ensures, that only the dependencies are considered, which the
project directly depends on and therefore tools like 'vim-hsimport'
can only consider the modules of these dependencies.
Add options '--allsections' and '--ignore=FIELD'
Consider specified fields
Update golden files for the addtition build-depends field
Add tests for options '--allsections' and '--ignore=FIELD'
Update README
cabal-cargs 0.4