Add clanvas directory which will contain rcfile and future files for caches, history, etc.

[rowdyrotifer]

Currently, if we want to add command history, or any sort of cache that persists longer than a session, we would need to choose more arbitrary files / locations to put them in. Instead, let's start by making this a configurable directory.

Check for an environment variable called CLANVASHOME, if it is set, then use that value.

Otherwise / by default set this value to a .clanvas folder in the user's home directory.

In order to consolidate the growing number of files, move ~/.clanvasrc to clanvas_data_directory/rcfile.

On startup, if this directory does not exist, create it. Also on startup, if the rcfile does not exist, create it (but leave it empty).