symlink mib hrl output in apps `include' directories

upgrade certifi to latest release

this restores compatibility with rebar2 and erlang.mk

fix tupple merging for realsies.

Full rewrite, code should be understandable now.

Tup merge tests

- proper segregation of comparison between tuple terms and non-tuple
  terms. Guards weren't specific enough and that meant the wrong clauses
  of guards would be triggered
- proper deduplication of entries in the list. An additional N passes
  are required (we co-opt the reverse step to be more efficient) because
  while the original lists:umerge easily removes dupes, this is
  requiring more logic here since `[a,{a,b},{a,b,c},a,{a,b,c}]` is a
  possible interleaving and we'd want `[a,{a,b},{a,b,c}]` -- comparison
  of direct neighbours isn't enough.

(the tests fail)

Fix a small bug in the MIB compiler when building dependencies

Default to no eunit formatter if verbose specified

The previous default meant that verbose output would not be emitted.

fetch eunit_formatters config not from the command args but from the config

When compiling a dependency with a MIB file the generated hrl file is left in
the root project directory in a file called "include". This has the perverse
effect of messing up the search path for include files causing any dependencies
with files in their "include" directory to fail to build after that.

auto-update the registry if a pkg isn't found, fail if it still isn't found

remove backward_compat entry from travis s3

special handling of relx configs in profiles

Relx config need new values at the end of the list and
profile additions prepended. So now in apply_profile in
the case it is a relx config we prepend the config list.
This does, however, mean that a profile release can not
'extend' a release defined in the default profile since
the one being extended would have its definition after
the profile release and thus relx would not be able to
use its values for extending.

preserve attributes when copying files in rebar_utils:cp_r for unix

don't add a provider if the same namespace and name already exists

Handle force flags in leading position

The checking of flags and the parsing of arguments is separated up.

Ct output improvements

- eunit assert look better
- lager logs to the html logs

upgrade eunit_formatters to 0.3.1 for OTP18 bug fix

only add package list of versions to registry if it has the right build tool support

upgrade eunit_formatters for OTP 18 support

warn on incorrectly specified test options in `rebar.config`

when `ct_opts`, `eunit_tests`, `eunit_first_files`, `ct_first_files`, `erl_first_files`,
`eunit_compile_opts`, `ct_compile_opts` and `erl_opts` have values that are single non-list
terms warn and try wrapping them in a list when processing them in the `eunit` and `ct`
providers

Fix error reports on missing include paths

In some cases (nested includes?) paths end up in such a way that joining
them breaks up and hard-crashes rebar3. This patch specifically handles
this scenario to fix things by avoiding passing empty lists to
filename:join.

Update cf