add .0 to avoid implicit conversions float->int
DiLeptonMatrixMethod: refactor and add getRelStatError

Move the code getting the histo to a separate function
(`getHistoAndParametrization`), which can be reused. Define
getRelStatError (relative errors should be added in quadrature).
bugfix : getStatError -> getRelStatError

getRate always expects a relative error since it does rate*(1+epsilon)
However, the stat err from the histogram was fed as an absolute error.
This is still not the correct thing to do when adding in quadrature
all the different error sources, but it's good enough for a test to
just check the new errors (which are all included in the error bar of
the matrix, i.e. adding in quadrature only one source).
matrix with both mu,el split in HF/LF; sf after pt>20
test_DiLeptonMatrixMethod : also print two syst
add fraction uncertainty
add matrix with composition variations
Merge branch 'update-wh-sys'

Conflicts:
	Root/DiLeptonMatrixMethod.cxx
	SusyMatrixMethod/DiLeptonMatrixMethod.h