Squashed 'cInterpol/newton_interval/' content from commit 0dde794

git-subtree-dir: cInterpol/newton_interval
git-subtree-split: 0dde794483ceebb0160de1db8f718924b3e89003
Merge commit '64a76d8f98c7a44e5dbb107d62ac3ba061dd39d4' as 'cInterpol/newton_interval'
Refactored tests to suit newton_interval subtree and moved test_fornberg to finitdiff package