Bump version to 0.3.4

This change bumps the version of the crate to 0.3.4. The following
notable changes have been made since 0.3.3:
- Optimized runtime performance and decreased asymptotic time complexity
  of core data base operations
- Introduced --help/-h options to display help text
- Added GitHub Actions workflow for publishing the crate

Author: d-e-s-o

CHANGELOG.md

@@ -1,5 +1,5 @@
-Unreleased
-----------
+0.3.4
+-----
 - Optimized runtime performance and decreased asymptotic time complexity
   of core data base operations
 - Introduced `--help`/`-h` options to display help text

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "notnow"
-version = "0.3.3"
+version = "0.3.4"
 edition = "2021"
 rust-version = "1.65"
 authors = ["Daniel Mueller <deso@posteo.net>"]