Parse config file and act upon

All dependencies were updated.

An example configuration file `config.yml` is added to show the
configuration options. Following locations are checked:
- `/etc/webhookey/config.yml`
- `<config_dir>/webhookey/config.yml`
- `./config.yml`

Whereas `<config_dir>` is depending on the platform:
- Linux:   `$XDG_CONFIG_HOME` or `$HOME/.config`
- macOS:   `$HOME/Library/Application Support`
- Windows: `{FOLDERID_RoamingAppData}`

Each hook's action is executed if all of the specified filters match.

Cargo.toml

@@ -9,3 +9,7 @@ rocket = "0.4"
 rocket_contrib = { version = "0.4", default-features = false, features = ["json"] }
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
+serde_yaml = "0.8"
+regex = "1.4"
+dirs = "3.0"
+anyhow = "1.0"