Add "re1_5_" namespace prefix to regexp compile, etc. functions.

To ease integration with other projects, i.e. avoid namespace conflicts.
Besides just adding prefix, naming was generally cleaned up (both for
functions and files). Note that while prefix is "re1_5_", original re1
naming convention still holds for the rest of name - that is, words joined
without any delimeter or capitalization.
Add "re1_5_" prefix to regex execution functions.