Improve accuracy of ROC (and DET) plots

Internally computes roc using both far and frr values for more
accurate plots.
Fixes #60 and #58
2 jobs for roc-fixes in 8 minutes and 34 seconds (queued for 8 seconds)
Status Job ID Name Coverage
  Build
failed #167883
docker
build_linux_36

00:08:32

84.0%
failed #167884
macosx
build_macosx_36

00:05:51

84.0%
 
Name Stage Failure
failed
build_linux_36 Build
TOTAL                                   1438    227    84%
----------------------------------------------------------------------
Ran 21 tests in 23.688s

FAILED (failures=1)
Tests failed for bob.measure-4.1.1b0-py36h51386b0_0.tar.bz2 - moving package to /scratch/builds/bob/bob.measure/miniconda/conda-bld/broken
WARNING:conda_build.build:Tests failed for bob.measure-4.1.1b0-py36h51386b0_0.tar.bz2 - moving package to /scratch/builds/bob/bob.measure/miniconda/conda-bld/broken
TESTS FAILED: bob.measure-4.1.1b0-py36h51386b0_0.tar.bz2
ERROR: Job failed: exit code 1
failed
build_macosx_36 Build
TOTAL                                   1438    227    84%
----------------------------------------------------------------------
Ran 21 tests in 23.404s

FAILED (failures=1)
Tests failed for bob.measure-4.1.1b0-py36hae442a8_0.tar.bz2 - moving package to /Users/gitlab/builds/b6d3167a/0/bob/bob.measure/miniconda/conda-bld/broken
WARNING:conda_build.build:Tests failed for bob.measure-4.1.1b0-py36hae442a8_0.tar.bz2 - moving package to /Users/gitlab/builds/b6d3167a/0/bob/bob.measure/miniconda/conda-bld/broken
TESTS FAILED: bob.measure-4.1.1b0-py36hae442a8_0.tar.bz2
ERROR: Job failed: exit status 1