Support for the XDG Base Directory Specification

[logological]

Currently, CGTerm expects its configuration file to be located at $HOME/.cgtermrc. It would be better if CGTerm instead followed the XDG Base Directory Specification. This is an increasingly popular standard (or set of best practices, if you prefer) defining where applications should look for and store user-specific configuration files and other data. The advantage of using this specification is that the user's home directory becomes less cluttered with arbitrarily named dotfiles and hidden directories.

To implement the specification, I think all CGTerm would need to do is put the configuration file in $XDG_CONFIG_HOME/cgtermrc, or $HOME/.config/cgtermrc if $XDG_CONFIG_HOME is empty or unset. (If desired, it could continue to look for $HOME/.cgtermrc as a fallback.)