This replaces all deprecated function usage by alternative ones based on
a version switch enacted at compile time, preventing all warnings.

This will likely introduce some possible runtime errors in using a
Rebar3 compiled on OTP-20 or OTP-21 back in versions 19 and earlier, but
we can't really work around that.

A bunch of dependencies have been updated to support OTP-21 without
warnings as well.

Get more up-to-date root certs. This was blocked for a while because
certifi wouldn't build on windows, but this is now fixed, with minimal
changes to the use case -- only a small change in the bootstrap script
is required.

The new certifi lib is also a few megabytes lighter than before, which
is good for rebar3.

Includes Relx fixes

Signed-off-by: Fred Hebert <mononcqc@ferd.ca>

Patches:

- Try to start epmd when distribution fails
- Allow non-default profile deps upgrade
- Switch default license in templates to Apache 2.0, and hook it up in
  the .app file
- Fix git SHA comparisons for dep update
- Let relx know about rebar-specified erl_opts
- Use rm_rf instead of ec_file:delete, fixing some deps-related issues
  on Windows
- Handle internal CT failures
- Fix profile merging of erl_first_files options
- Fix CT output in skipped test cases and failing end of function
  hooks
- Officially drop R15 support, since its SSL libs can no longer talk
  to hex.pm
- REBAR_COLOR supports all ec_cmd_log intensity options, allowing the
  none value to disable all colors without dropping termcap support
- Bump relx to 3.22.4

The one new feature supported here is for the interactive shell:

- Support commands in the shell such as r3:Command(),
  r3:Command("--args=as a string"), or r3:Command(Namespace, "--args=as a
  string"), instead of just r3:do(Command).

- [OSX tests added to CI](https://github.com/erlang/rebar3/pull/1471),
joining linux and windows 10
- [upgrade relx to 3.22.3](https://github.com/erlang/rebar3/pull/1518),
[fixing multiple
issues](https://github.com/erlware/relx/releases/tag/v3.22.3)
- [Fixing eunit errors in 19.3 when `init_per_*` isn't paired with
`end_per_*`](https://github.com/erlang/rebar3/pull/1516)
- [Allow single test spec in
ct_opts](https://github.com/erlang/rebar3/pull/1506)
- [Properly warn when missing inets at
runtime](https://github.com/erlang/rebar3/pull/1505)
- [rebar_utils:escape_chars handles quotes in
paths](https://github.com/erlang/rebar3/pull/1504)
- [Fix typo in help text for upgrade
command](https://github.com/erlang/rebar3/pull/1503)
- [change package version warnings to debug
level](https://github.com/erlang/rebar3/pull/1502)
- [Path-type sensitive .cmd creation for
escripts](https://github.com/erlang/rebar3/pull/1500)
- [Windows escripts get cmd
autogenerated](https://github.com/erlang/rebar3/pull/1494)
- [REBAR_CONFIG impacts config file for project root
only](https://github.com/erlang/rebar3/pull/1497)
- [Fix wildcard usage in rebar3
clean](https://github.com/erlang/rebar3/pull/1498)
- [Bump cth_readable to
1.2.4](https://github.com/erlang/rebar3/pull/1496) (fixing some
erroneous reports when suites get skipped)
- [Add respect for src_dirs option in app_discover and
app_info](https://github.com/erlang/rebar3/pull/1486)
- [Add support for global plugin-defined
templates](https://github.com/erlang/rebar3/pull/1473)
- [catch badarg exception from eunit in
`rebar_prv_eunit`](https://github.com/erlang/rebar3/pull/1472)

This also patches up a problem for hooks when dealing with directories
with spaces in them, and reduces complexity of bootstrap file.

This detects existence of Hex registry at
$HOME/.cache/rebar3/hex/default/registry and skips "rebar3 update" step.
It also detect presence of bootstrap dependencies in _build/default/lib/
and skips fetching them.

fix #790