Set version to 2.7.0, changelog and doc-deps update.

Set version to 2.6.0.

Set version to 2.5.1.

Set version to 2.5, update CHANGELOG, compat with JSON@1.

Set version to 2.4.0.

Set version to 2.3.1.

See github.com/fredrikekre/Literate.jl/releases/tag/v2.3.0 for releas…

…e notes

See github.com/fredrikekre/Literate.jl/releases/tag/v2.2.1 for releas…

…e notes

See github.com/fredrikekre/Literate.jl/releases/tag/v2.2.0 for releas…

…e notes

See github.com/fredrikekre/Literate.jl/releases/tag/v2.1.1 for releas…

…e notes