Add main command-line orchestration implementation

This adds the main module, supposed to be interacting with the other
modules, providing printing, event handling and termination handling.

The implementation is growing, but I think it's reasonably clean.
Add structure for content aware downloading

This adds the structure needed for "content aware" downloading, in the
sense that we'll be trying to extract resource links from post links. It
also patches the events and logic to match the expected API used in the
`cli` module.
Refactor and update reddit

This adds event emitting and the correct `saved` implementation, which
is well encapsulated and only does one thing - though it signals the
event.
Bump version to 0.1.0

This is the first "functional" release. It actually is able to fetch
links, though it only downloads images with a very rudimentary filter.