Rename monadic helper functions for consistency
Rename monadic helper functions for consistency

Renames `optAppend` and `optPrepend` to `mAppend` and `mPrepend` to
reduce the amount of churn when creating new test suites.

Also moves `append` and `prepend` to the centralized Functions file
since these won't need to change for other types.

ojolabs/Runes,stevebrambilla/Runes,DarthMike/Runes,ikesyo/Runes,DarthMike/Runes,alvinvarghese/Runes,bruceflowers/Runes,stevebrambilla/Runes,ikesyo/Runes,ojolabs/Runes,thoughtbot/Runes,ojolabs/Runes,RuiAAPeres/Runes,alvinvarghese/Runes,alvinvarghese/Runes,alvinvarghese/Runes,thoughtbot/Runes,DarthMike/Runes,bruceflowers/Runes,thoughtbot/Runes,RuiAAPeres/Runes,bruceflowers/Runes,RuiAAPeres/Runes,ojolabs/Runes,ikesyo/Runes,stevebrambilla/Runes,DarthMike/Runes