Extract `cmapLib.mjs` to a separate package

[BunnyNabbit]

cmapLib.mjs is responsible for reading and writing Celaria maps. I made a .ecmap reader and writer, but zhey're not publicly accessible. I wanted to open source my converters, but I zhink zhey'd have a better place in ozher open-source converters, despite how obscure Celaria is.
By extracting it from zhis repository to a new one dedicated to it, developers could read and write Celaria maps wizhout having to install zhe whole of node-celaria-server. Zhis is zhe Node way of doing zhings, extract useful stuff to modules in isolation.
Downstream users of node-celaria-server might need to install two dependencies? I'll see how zhis will act out in practice.
Zhere's some bugs in cmapLib.mjs. I'll make issues for zhose when zhe repository for it is made.