7.5.0: features and logs

• Log format (debugs and warnings) changed as part of the upgrade to watchexec 1.14
• WATCHEXEC_* environment variables are not set for subprocesses anymore. I didn't actually intend to have them in the first place, but chime in if you rely on them!
• #152 New --features option to pass the --features flag to a selection of cargo commands that support them. E.g. cargo watch --features feat -x check -x test can now be used instead of cargo watch -x 'check --features feat' -x 'test --features feat'.
• Also fixes a bug where a polling message was shown even when --quiet was given.