Remove "is" prefix from boolean methods
Remove TODO comments; remove colons from others
Remove unused import
Add simpler string replacement
Target spec version 0.10

The jgm/CommonMark repo contains incomplete changes to the spec which we shouldn't test against.  The absence of a specific version has caused numerous failed builds due to this.
Merge remote-tracking branch 'origin/code-cleanup'
Merge remote-tracking branch 'origin/spec-version'