Basic escaping is done only. Fancy hex sequences are not covered, but
this should otherwise take care of the most common issues.

Fixes #497

This reverts commit b06a6ecadd.

The wide-cast catching of undef errors would make it so any provider
calling an undefined function would be reported as a missing 'do' for
the provider.

This patch inspects the stacktrace to know if `Provider:do/1` is indeed
the missing callback, and reports the rest properly.

This tries to reduce memory usage when running `rebar3 shell` by running
the agent in the current process (and avoiding to copy state
cross-boundaries), and using frequent hibernation after each run to
force a full GC and compaction of the current process.

and replace with `cover_opts`

The old run didn't necessarily apply all profiles well, and would only
reload modules in the app file. However, since adding extra_src_dirs,
modules can be compiled without ending up in the app file; this lets
the rebar3 shell agent handle that case.

to itself so a selective receive can be used to retrieve it

fixes #547