added dihedral calculation for all the chi angles (chis 1-4 )
modified chi calculations to the updated MDTraj codebase
modified chi calculations to the updated MDTraj codebase
fixed the function compute_chi_all
 added definitions to docstring
fixed return as type int for residue ids
Merge pull request #224 from raviramanathan/master

added dihedral calculation for all the chi angles (chis 1-4 )