Add support for YAML format configuration files. In addition, this
commit adds instructions about YAML config files to the README, and it
also changes the README to encourage use of YAML instead of JSON.
This commit introduces an additional option for extended configuration
syntax for linking. It adds the "create" parameter which results in
automatically creating a parent directory if necessary before linking a
file.
This commit introduces an extended configuration syntax for linking
files and directories. Currently, this syntax allows for specifying
items to be forcibly linked, overwriting existing files or directories
if necessary.
The extended configuration syntax was proposed by Travers McInerney
<travers@mcinerney.me>.
