Skip builds on specific CI systems

Most CI systems will not build if a git commit message includes a string like [skip ci]. For example:

git commit -m "update install docs [skip ci]"

When testing out a particular CI system, some CI systems allow skipping their particular CI. For example, if testing out new AppVeyor systems, skip building on Travis-CI by including

[skip travis]

in the git commit message.

Skip strings

For each CI system include the string in git commit -m or similar git commit message.

Generic skip only

At the time of this writing, these CI are known only to support the generic [skip ci]: * CircleCI supports [skip ci] * GitLab supports [skip ci] * Bitbucket support [skip ci]