Enable reloading config while running

Use SIGUSR1 or the helper command `swaybar-commander reload` to trigger
a config reload.
Create update chan as part of block
Replace deprecated function calls
Update sample block to correctly handle volume=0

Print 0 instead of nothing.
Update samples to what I currently use
Re-word contributing section
Add link to project home page
Correctly label as swaybar status command
Add sample blocks
Link to git repo, not project home
Allow an update requester command for each block
Add helper command to easily request block updates
Ignore build artifacts
Allow triggering block updates with signals
Add doc comments
Change 'refresh' to 'update'
Create initial basic version

- Run blocks at a specified interval, and only actually send updates to
  swaybar as needed.

- Load configuration from a TOML config file.