Improve error handling in ct provider

support single atoms for pkg deps, fetch highest version available

Warn on bad use of include_lib but try to find the header anyway

disallow suites in project root

fixes #331

rm old beams, make erlcinfo graph per app isntad of global to project

merge rebar2's Refactor logic and optimizations in rebar_erlc_compiler:doterl_compile/4 #467

fix build instruction

Remove global plugins

install dep plugins & run provider hooks the same as shell hooks (Rereopen 316)

Fix ns help

modify `ct` provider to copy selected directories and compile them

alongside their source (ie, if `some_tests` is a directory that
contains test suites beams resulting from compiling them will be
placed in `some_tests` in the appropriate `_build` directory

update the dir used for upgrade deps to the new path under _build