Add method for easily adding inline scipts

[samuell]

Similar in to #124 , we should have a method that simplifies adding inline scripts to be executed as a script file in various languages. The syntax could be:

pythonProc := wf.Script("python", `
import pandas as pd
import matplotlib.pyplot as plt

df = pd.read_csv("{i:some_infile}")
df[df["value"] >= 0.5].plot()
plt.savefig("{o:figure}")`)
pythonProc.SetOut("figure", "my_plot.png")

... etc.