Add bindings for astyle to c.vim

These bindings will also work for cpp files. The bindings are:
    * Q uses astyle to format code
    * In visual mode, = uses Q, and then re-indents with vim's built in
      indenter (as astyle indents the first line to 0 when using visual
      selection)
    * <Leader>ff calls astyle on the whole file instead of =