Started to implement the monoid version of finger tree.

Invented quite fancy way of implementing the monoid
and measure type classes as interfaces. Everything
still compiles and tests pass.
Intermediate commit.

Does not compile. Need to continue tomorrow.
Finished the finger tree implementation by adding the sequence.

Need to add tests and comments to the new collections next.
Converted tests to Sequences and debugged them.

After a sweaty debugging session Sequence<T>
seems to now work according to basic tests.