Hex improvements

add project_providers after initing default providers but allow overrides

Add me to THANKS for suffering through Tristan's code

Add more version constraints

Allow for any number of whitespaces after compairison opperator

Improve updating and error printing

Fix failing tests

Support --setcookie option

Replicates `erl` behaviour.

give top level plugin providers precedence over default providers

The new version fixes parse transforms over OTP incompatibility that
would crash entire compile runs before.

Make lock files future-proof

break up do/1 function in install_deps to make upgrade less confusing

upgrade relx to 3.17.0

set default color intensity to high

update relx to 3.16.0 to include color intesity update

Less color

Changes to how hex or packages may work in the future will necessarily
bring changes to the format of lock files.

This commit adds an optional framing for future lock files of the form:

    {Version, LockList}.
    <Whatever consultable attributes>

This format is supported such as the LockList is the current lockfile
contents, and will never have more information than it currently does.

Attributes can be whatever and are currently undefined.

Rebar copies will be able to:
- Keep using the core locklist (which avoids breaking the last year or
  so of community libraries using rebar3)
- Warn when it runs an outdated copy in comparison to the lock file
- Automatically rewrite lock files in the format it supports
- Augment or parse files in a version-specific manner.

This changes the usage interface slightly, but is backwards *and*
forwards compatible.

Add secondary hook for rebar_prv_compile

The provider is used for debugging to help displaying current rebar's state.

Usage:
  rebar3 state

upgrade relx to 3.15.0

Add test case for relx overlay vars

Ignore unknown warning when dialyzer < 2.8

Makes use of several var types: integers,
strings, binaries, binary strings and tuples.

check top level config for minimum or blacklisted  otps at start

erlc_compile, for before/after compiling .erls to
.beams, but before .app.src to .app

add user-agent to http request headers