Add Erlang support

[kazk]

Erlang/OTP 20.0, test integration with EUnit. Uses rebar3, no packages are installed for now.

-module(fib_tests).
-include_lib("eunit/include/eunit.hrl").

fib(0) -> 1;
fib(1) -> 1;
fib(N) when N > 1 -> fib(N-1) + fib(N-2).

fib_test_() ->
  {"Fib",
    [{"works for some inputs",
      [?_assertEqual(1, fib(0)),
       ?_assertEqual(1, fib(1)),
       ?_assertEqual(2, fib(2)),
       ?_assertEqual(3, fib(3)),
       ?_assertEqual(5, fib(4)),
       ?_assertEqual(8, fib(5))]},
     {"fib(31)", ?_assertEqual(2178309, fib(31))},
     {"fib(-1) errors", ?_assertException(error, function_clause, fib(-1))}]}.

<DESCRIBE::>Fib

<DESCRIBE::>works for some inputs
<IT::>Unnamed Test
<PASSED::>Test Passed
<COMPLETEDIN::>0
<IT::>Unnamed Test
<PASSED::>Test Passed
<COMPLETEDIN::>0
<IT::>Unnamed Test
<PASSED::>Test Passed
<COMPLETEDIN::>0
<IT::>Unnamed Test
<PASSED::>Test Passed
<COMPLETEDIN::>0
<IT::>Unnamed Test
<PASSED::>Test Passed
<COMPLETEDIN::>0
<IT::>Unnamed Test
<PASSED::>Test Passed
<COMPLETEDIN::>0
<COMPLETEDIN::>18

<IT::>fib(31)
<PASSED::>Test Passed
<COMPLETEDIN::>126

<IT::>fib(-1) errors
<PASSED::>Test Passed
<COMPLETEDIN::>0

<COMPLETEDIN::>150

Note that tests without desc attribute (derived from annotations like "fib(31)", called titles in EUnit terms) are named "Unnamed Test".
This is because:

• Generating a name from source (module, function, arity) and id (list of integers) attributes can result in unexpected names
• Generating a name from the "parent" group is difficult because some macros produces groups without desc

Also note that groups without desc are ignored in the output because it's hard to differentiate from groups generated by some macros.

---

Closes #474
Closes #46