Bump version to 0.3.0

This change bumps the version of the crate to 0.3.0. The following
notable changes have been made since 0.2.6:
- Changed task storage format:
  - Switched from single-file-for-all-tasks scheme to having one task per
    file (identified by 128 bit UUID)
  - Switched from using custom JSON serialization format to relying on
    interchangeable iCalendar TODO events
  - Added support for only saving tasks that were changed
- Added support for finding the currently selected task on other tabs
  via '*'
- Added example program using automatically generated task data
- Overhauled error reporting mechanism, now reporting error chains
- Made tag to toggle through UI user-configurable and no longer hard
  wired to task completion
- Re-select task after successfully editing tags
- Use Unicode aware lowercase in task summary search
- Fixed reverse task search not progressing under certain conditions
- Switched to using GitHub Actions as CI provider
- Bumped minimum supported Rust version to 1.65
- Bumped dirs dependency to 4.0

CHANGELOG.md

@@ -1,5 +1,5 @@
-Unreleased
-----------
+0.3.0
+-----
 - Changed task storage format:
   - Switched from single-file-for-all-tasks scheme to having one task per
     file (identified by 128 bit UUID)

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "notnow"
-version = "0.2.6"
+version = "0.3.0"
 edition = "2021"
 rust-version = "1.65"
 authors = ["Daniel Mueller <deso@posteo.net>"]