Add support for ~ references to home directories in Include

[spladug]

In ssh_config(5) it says:

each pathname may contain glob(7) wildcards and, for user configu‐
rations, shell-like ‘~’ references to user home directories.

This adds support for expanding the ~ into the path for the user's home directory when not parsing a system config.

[kylelemons]

Hey @kevinburke ! Any chance we can get your thoughts on this? We rely on this package for an internal tool and a number of users have stumbled over this.