get-rc: get options from the '~/.ggspecrc' file

... if it exists and contains any options.
main: implement 'rc' file functionality

Ggspec now supports reading from a '~/.ggspecrc' file. Should work on
Unix, Mac, and Windows. The '.ggspecrc' file format is very simple: it's
_literally_ the same as the command-line options format, with the bonus
that anywhere you would use a space to separate options you can use
either a space or a newline. This allows me to just use the 'getopt'
library functions to parse it instead of yet another module.

So right now mine looks something like this:

  -c
  -f normal

Order of precedence is command-line options first, then 'rc' file
options.

Comments are not supported yet.
Merge branch 'master' into guile-2