Collecting $dE/dx$ histograms

The first step in the analysis is to run through the micro-DST and collect $dE/dx$ information for fitting. The macro that is used to do this is fill_contain.C and the output is a ROOT file with a T49Container which contains a list of histograms of $dE/dx$ and the number of $dE/dx$ points in each bin. The histograms are made in bins of charge, $\log{p}$, $p_T$ and azimuthal angle $\phi$. The default binning is 0.1 GeV in $p_T$ and 20 bins in $^{10}\log{p}$ between 0 (1 GeV) and 2 (100 GeV). The binning in $\phi$ is 8 bins, but only four of those are filled, due to the 30 cut on $\phi$.