Add Makefile template for new projects

[oubiwann]

I've had so many issues with with the rebar3 LFE REPL (just ran into a new one this week, due to Erlang 26.0) and have had numerous bug reports over the years -- many of which can't be addressed because it's not really the LFE REPL that's running. Rather, it's some very clever hackery that rebar3 does to support arbitrary/custom shells.

I want to continue supporting rebar3 lfe repl, but I'd also like to offer an OS-process alternative for folks.

Add targets for:

• clean
• hex publish
• build (rebar3 compile alias)
• repl (accepts a PROFILE= env var and starts the REPL with the associated deps)

Note that this ticket is partially inspired by #66.