Feature/pr214 Appendable to output and error streams - changes

[Euklios]

I can't (or don't know how to) edit a pr from another person. Here are the changes from #214 as specified in the review from @bramp.

Changes:

• Rename processInputStream to processOutputStream, in order to reflect the actual code flow and defaults
• Initialize process(Input/Output)Stream to use System.out and System.err as defaults
• Add Precondition to process(Input/Output)Stream
• Remove the fallback for null values of process(Input/Output)Stream (no longer needed)
• Cleanup import as specified in comment
• Make errResource final

Additionally, I've merged the current head to this branch and resolved conflicts

[bramp]

Looks good. Thanks.