Upgrade to 0.15.1

[jburgy]

Attempt to resurrect this awesome project. zig build test currently failing with

test
└─ compile test Debug native 1 errors
ctregex.zig:759:37: error: use of undefined value here causes illegal behavior
                        if (this_cp >= range.start and this_cp <= range.end)
                            ~~~~~~~~^~~~~~~~~~~~~~

[jburgy]

Removing [WIP] tag per this convo