Add file configuration.

Add --config option to read a file other than the default user specific
config file.

If a --config option is not given read a config file which is ignored if
it doesn't exist.
On Windows the config file is in %APPDATA%/.sphiarc
On Linux/BSD/etc the cofnig file resides at $HOME/.sphiarc

SPHIA_PATH is given the top priority if given, instead of only being used
if no other path option is set.
Add back BIN option for named binaries

The default config file we look for uses the binary name when compiling.
Add config options to man
If .sphiarc exists in the current directory use it, if not use the
default user config.

Added a file_exists function to check for existance.