Release version 0.5a

* Track `expl3` changes (#30)

Release skmath v0.5

Bump version to 0.4b

Bump version to 0.4a

Bump version to 0.4, update documentation PDF

Omit implementation from docs (due to urdh/skdoc#30), bump version

Bump version to 0.3a

Include updated documentation for 0.3

Merge branch 'master' of github.com:urdh/skmath

Merge branch '0.1h'