Gets in line with more common usage of the wording, as discussed in
issue #1421 and
https://www.reddit.com/r/erlang/comments/6sd01p/help_terribly_frustrated_with_the_erlang_build/

This is done through 3 main change groups:

- replacing `~s` by `~ts` in format strings, so that strings that
  contain unicode are properly printed rather than crashing
- adding the `unicode` argument to all function of the `re` module to
  ensure transformations on strings containing unicode data are valid
  instead of crashing (see issue #1302)
- replacing `ec_cnv:to_binary/1` and `ec_cnv:to_list/1` with matching
  functions in `rebar_utils`.

The last point has been done, rather than modifying and updating erlware
commons, because binary and list conversions can be a contentious
subject. For example, if what is being handled is actually bytes from a
given binary stream, then forcing a byte-oriented interpretation of the
data can corrupt it. As such, it does not appear safe to modify erlware
commons' conversion functions since it may not be safe for all its
users.

Instead, rebar3 reimplements a subset of them (only converting
atoms and chardata, ignoring numbers) with the explicit purpose of
handling unicode string data.

Tests were left as unchanged as possible. This may impact the ability to
run rebar3's own suites in a unicode path, but respects a principle of
least change for such a large patch.

The default license created with rebar3 templates is a BSD 3 clause
license. However the .app.src file generated do not include the license
there.

This adds the license type, fixing #1447.

This family of IDE with Erlang plugin is already quite popular.

Used a nonexisting option instead of a correct one

Issues formerly were avoided by quoting atoms. Unquoting them created
unbalanced tags (`{{{name}}`) which were mistakes. This patch inserts
spaces to unconfused bbmustache.

hex.pm is now using maintainers instead of contributors in metadata.
Templates should be updated to reflect it.

Some templates like OTP apps are usable within releases, so the text
does remain a bit vague, but hopefully less than before.

- The OTP app template now adds the supevisor
- The default apps_dir value does not contain the trailing '/' that the
  template index already added.

The first variable can be unkeyed and the provider will sub in the
variable name 'name'. Additionally, the built-in templates and
documentation have been updated so that 'appid' is now 'name' and the
alternative commands are shown.

This totally breaks compatibility with rebar2, and maybe it shouldn't
have.