ucsc-xena-wasm v1.12.0

UCSC Xena wasm utils

wasm methods to support UCSC Xena.

Build requires emscripten and 'make'.

emscripten is extremely unstable. Most versions will fail to build.

We currently build with sdk 1.39.3. See this thread:

https://github.com/emscripten-core/emscripten/issues/9797