migrate cli to clap v3 (#51)

* update cli to clap v3

* update changelog

CHANGELOG.md

@@ -8,6 +8,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 - Fixed handling of time zones so that they are now implemented properly ([#41](https://github.com/mfreeborn/heliocron/issues/41)).
 
+### Changed
+- Migrated from old version of `structopt` to `clap` for command line argument parsing.
+
 ### Removed
 - `--date-format` flag has been removed as it adds additional complexity when validating command line args for no real benefit.
 

Cargo.toml

@@ -3,7 +3,7 @@ name = "heliocron"
 version = "0.6.1"
 authors = ["Michael Freeborn <[email protected]>"]
 description = """
-Heliocron is a command line application written in Rust capable of delaying execution of other 
+heliocron is a command line application written in Rust capable of delaying execution of other 
 programs for time periods relative to sunrise and sunset.
 """
 documentation = "https://github.com/mfreeborn/heliocron"
@@ -24,9 +24,9 @@ integration-test = []
 [dependencies]
 chrono = "0.4"
 dirs = "2.0"
-serde = {version = "1.0", features = ["derive"]}
+serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
-structopt = "0.3"
+clap = { version = "3.1", features = ["derive"] }
 tokio = { version = "1", features = ["full"] }
 tokio-walltime =  "0.1.2"
 toml = "0.5"