This adds some more convolution to command parsing, unfortunately, but
makes some cases clearer (`rebar3 as as as as` is no longer valid). It
unfortunately disallows using $REBAR_PROFILE along with `as` in a rebar
command.

fixes #238

* Return error on failed and/or auto skipped tests
* Print all results for quiet repeated tests
* Sum results of repeated tests

Previously dialyzer stored the project PLT in ./build/, which meant the
same PLT was used for all profiles. This could mean partial rebuilding
of a PLT when switching between profiles.

fixes #216 and #220

rebar state from propogating appropriately

to `as` used to generate them

- fetch more complete refs for tags (may download more history than
  required, but it works)
- Fix comparison of tag distance by using lists everywhere

pre-purging before checking to facilitate long do chains

source files in the `compile` key of `module_info/1` so `rebar cover`
struggles locating source in some instances. in these cases a warning
is printed and crappy coverage info is written rather than none at all

`rebar.config` or via the `-c\--cover` flag given to the appropriate
task) from the `eunit` and `ct` tasks and add a `cover` task to
write coverage analysis to disk