Allow relative paths in docset configuration

[acook]

Absolute path is stored literally in configuration file.

It doesn't seem that Zeal has the ability to read ~, environment variables, or relative paths in its configuration.

This means that the absolute path to docsets is stored directly in the config file.

This reveals the username of the author, for those of us that share our configurations (publicly or otherwise), but also prevents configurations from being shared among groups and site deployments.

This also prevents the standard symlink for default config pattern when setting up multiple users on the same machine.

So, it would be nice to find a way around this. Relative paths from the user directory is just one possible solution.