Prepare release 4.0.0

[CraZySacX]

• Updated README.md with 4.0.0 breaking changes.
• Updated lib.rs with some additional information.
• Updated Cargo.toml.
• Fixes Consider using git2 instead of executing git process #15

[codecov]

Codecov Report

Merging #35 (dc1e7a1) into master (6dafdef) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master       #35   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           11        11           
  Lines          492       492           
=========================================
  Hits           492       492           

Impacted Files	Coverage Δ
src/lib.rs	100.00% <ø> (ø)

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