Generic polynomial function

[DryRun]

Added a function that makes polynomials for TF1s:

def polyn_msd_pt(nrho, npt):
    def fun_msd_pt(x, par):
        rho = ROOT.TMath.Log((x[0]*x[0])/(x[1]*x[1]))
        pt = x[1]
        ret = 0.
        for i in xrange(nrho + 1):
            for j in xrange(npt + 1):
                par_index = i + nrho*j
                ret += par[par_index] * rho**i * pt**j
        return ret
    return fun_msd_pt

(similarly for rho/pt and rho functions)

Also, I converted all the indentation to four spaces. Sorry that it's impossible to read the PR because of this.

[DryRun]

I don't know if this tags people automatically, so @jmduarte -- I made this PR to your script which makes it a bit easier to generate the polynomials. Unfortunately, the diff is impossible to read since I also converted the mixed tab/space indentation to 4-tab spacing... sorry about that. The generating functions themselves start on line 1215.