Adds a basic IntegratorType protocol.
`integrate` returns the integral.
Test using appenders.
Append function.
Test using append().
Use += for extending mutable collections.
Implicit parameters.
sequence() uses Stream.generate directly.
Correct a test name.
Fix tests depending on Stream conformance to SequenceType.
Sequence does the full Stream sequencing itself.
Stream no longer conforms to SequenceType.
Add + to append onto immutable ExtensibleCollectionType instances.
Correct the documentation of +=.
Document +.
Rename the appending files.
Merge pull request #47 from robrix/appending

Appending