Dep conflict as error

use PRV_ERROR for formattable errors

Also expose it in rebar_api

The option {deps_error_on_conflict, true} will make it so conflicts in
deps being fetched interrupts the operation rather than just display a
warning.

Defaults to `false'.

The deps are sorted and merged, but the merge function merges lists, not
elements. This yields deps that are duplicated and ran for multiple
times.

We first add proper sorts so the keymerge is guaranteed to be fine, and
then do a dedup run to get rid of duplicates if they happen to be.

Fix #267, refactor as/do/namespace interactions

Breaking up initial call to parse from the ones deep inside the provider
parsing to do smarter namespace detection, added 'as' the ability to
look into these also, and cleaned up the code a whole lot that would
depend on implicit assumptions.

A side-effect is that 'do' is now valid for all namespaces, although it
can be overriden.

halt with 0 on successful run

get rid of compile workers

Store base PLT in ~/.cache/rebar3/

set jobs for all compile jobs

merge rebar config opts for parent like done for profiles

Fix typo in error message

fix debug format to avoid crash with custom template

error before:

===> Uncaught error: {'EXIT',
                             {badarg,
                              [{io,format,
                                [<0.23.0>,
                                 "\e[0;36m===> Skipping template ~p, due to presence of a custom template at ~s~n~n\e[0m",
                                 ["/home/mariano/.config/rebar3/templates/fn_app/fn_app.template"]],
                                []},
                               {rebar_templater,prioritize_templates,2,
                                [{file,"src/rebar_templater.erl"},{line,330}]},
                               {rebar_templater,find_templates,1,
                                [{file,"src/rebar_templater.erl"},{line,274}]},
                               {rebar_templater,new,4,
                                [{file,"src/rebar_templater.erl"},{line,47}]},
                               {rebar_prv_new,do,1,
                                [{file,"src/rebar_prv_new.erl"},{line,44}]},
                               {rebar_core,do,2,
                                [{file,"src/rebar_core.erl"},{line,129}]},
                               {rebar3,main,1,
                                [{file,"src/rebar3.erl"},{line,46}]},
                               {escript,run,2,
                                [{file,"escript.erl"},{line,752}]}]}}

Revert "disable smp in escript"

disable smp in escript

templater: return error, don't throw, if git or hg fail

symlink extra test dirs and compile from there instead of from root project

root project

compile source from the symlinked directories under `_build`

get correct compile paths included in module info

update sample config to remove unsupported rebar2 options

don't traverse into subdirectories looking for beams

update erlydtl compiler to output to _build, add simple test

Bump to alpha

Fix namespace regressions

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.

update all examples in providers to use rebar3

parse `rebar3 as foo, bar task` correctly

fixes #238

fix code path update for deps

escript provider