also allow to map to 0 or 1
better split
Merge pull request #17 from gpetruc/MultiSignalModel-extras-part2

Multi signal model extras part2
Merge pull request #18 from gpetruc/postfit-rebased

Pre and post-fit uncertainties
If the rate is below 1e-3, use scientific notation
Fix weight issue
Merge pull request #19 from gpetruc/fix-non-uniform-binned-generation

Fix weight issue
Merge pull request #20 from gpetruc/fix-low-rate-datacard-combination

Fix issue when combining datacards that have very low yields
fix crash on workspaces that didn't have discrete nuisances
Merge pull request #21 from gpetruc/fix-discrete-nuis-crash

fix crash on workspaces that didn't have discrete nuisances