Removed separate compilers
Resolves apps to build
Finds avail deps before pulling/building
Includes relx
Simplifies build commands

rebar's beam files are actually compiled by bootstrap's call to
make:files/2, so warnings_as_errors in rebar.config isn't really used.

* fix overlong lines
* where appropriate use %% instead of %

We use namespaced_types option to choose between dict() and dict:dict() types.

app_bin option was used by the install command which has been
removed in 51ed787.

eunit_test:function_wrapper/2 was renamed to eunit:mf_wrapper/2 in
R15B02. Ignore both calls like we do with escript:foldl/3.

1. manually insert directory entries to work around issues fixed in
   R15B02 erl_prim_loader
2. put the escript archive's beams in appname/appname/ebin

Tested with R13B03 and R15B01.

Rebar has support for optional compilers built-in. These compilers might
not be installed causing xref to return errors for the undefined external
function calls query. The updated filter list will catch this error and
act as a nop if they are installed.

The custom queries are configured in rebar.config via the tuple
{xref_queries, [{query(), query_result()},...]}.  The implementation
passes the query() string to xref:q and compares the return value with
query_result(). It will result in an error if they do not match.

The following configuration, for example, is the same as running the
xref check undefined_function_calls. It additionally filters
ejabberd_logger:*_msg/4 from the result as these functions are generated
on execution by ejabberd and not available at compile time.

{xref_queries, [{"(XC - UC) || (XU - X - B -
                 (\"ejabberd_logger\":\".*_msg\"/\"4\"))",[]}]}.

This patch also modifies the build process of this package by running a
custom query instead of doing a diff against a static xref_warning file.

Add no_debug_info option.
Remove debug_info=1 option.

to the OTP bin dir.