Make naming adhere to Rust API guidelines, docs, CLI help, dependencies bump

[virtualritz]

• Make naming adhere to Rust API guidelines.

  • get_ prefixes were removed where neccessary.
  • Some functions were renamed to reflect common practices found in modern crates.
  • Some traits were implemented to replace certain getters resp. allow more canonical use of the API. E.g. AsRef, TryFrom or From.
  • Some enum variants were renamed. I.e. SByte etc. became SignedByte etc. since the above API guidelines call for Sbyte otherwise, which is less easy on the eyes.

• Docs had newlines & missing periods added where necessary and spaces removed. The latter particularly before/after a slash '/').

  • On that note, I'm about to open a feature suggestion for rustdoc to add a hair space (U+200A) automatically before/after a slash.

    That has the nice side-effect that the browser will (line) break at the slash without having to add the eyesore that a full space before/after introduces. This is only relevant for long words separated by a slash anyway; i.e. not this crate.

    See e.g. the Wikipedia section about em/en-dashes for the same (introducing line breaks w/o adding visible spacing).

• Updated/fixed some CLI help/about messages.

• Bumped dependencies in Cargo.toml (& removed patch version) and bumped crate version to 1.6.0 to signal API breakage introduced by this PR.

[virtualritz]

This PR should also close #4.