P.S.: erlydt has a plugin that might be useful for porting over to this tool - it basically compiles stuff in priv/templates into *_dtl modules automatically:
https://github.com/tsloughter/rebar3_erlydtl_plugin
I wanted to put mine in the priv directory but couldn't figure out how to get that to work either. I tried setting the templates_dir mustache environment variable to my priv directory but I kept getting an error.
My .mustache templates are not being copied to the ebin when I use rebar3 :-(
I opened a SO question about it: http://stackoverflow.com/questions/36231976/how-can-i-include-a-mustache-file-in-erlang-release
P.S.: erlydt has a plugin that might be useful for porting over to this tool - it basically compiles stuff in
priv/templates
into*_dtl
modules automatically: https://github.com/tsloughter/rebar3_erlydtl_plugin