General maintainance.

* Update docstrings and function signatures.
* Follow python naming conventions as much as possible.
* Be consistent in the argument names.
* Require all methods to accept GUIDMixin as ID.
* Drop unused TimeoutError class.
* Purge exec flag from routingtable.py.
Setup initial testsuite; refactor abstract methods.

* Make abstract methods raise NotImplementedError; test most of them.
* Add initialization tests for abstract class.
* Follow python naming conventions.
Test and refactor initialization of RoutingTable implementations.

* Initialize superclasses properly.
* Use `super` instead of naming the superclass explicitly.
* Defer testing of other methods for now.
* Follow python naming conventions.
* Delegate logger instantiation to superclass.
Fix and abstract ID range. Test init attributes.

* Install an ad-hoc equality for KBuckets.
* Follow python naming convention.
Test and refactor kbucketIndex.

* Handle GUIDMixin transparently.
* Raise KeyError on key with bad range.
* Raise RuntimeError if kbucket invariant is violated.
* Include a hint for a possible optimization.
* Follow python naming conventions.
Test and refactor getContact.

* Handle GUIDMixin transparently.
* Ignore the docstring mentioning ValueError and
  test for a None value on unsuccessful lookup, as
  is the case throughout the code.
* Align signature with kbucket.GetContact and simplify code.
* Follow python naming convention.
Test and refactor removeContact(s).

* Make argument names consistent with rest of tested code.
* Leverage exceptions to simplify code structure.
* Add logging on exception.
* Follow python naming convention.
Test and refactor RoutingTable.distance.

* Raise ValueError if strings have unequal lengths.
* Handle guid.GUIDMixins transparently.
* Follow python naming conventions.
Test and refactor touchKBucket.

* Add ability to set timestamp manually.
* Test the abstract method, too.
Add and test numToId for easy conversions.

* Refactor _randomIDInBucketRange to use numToId.
* Abstract node ID length in constants.py
* Refactor distance to use node ID length, and raise
  an exception when either of the keys is of improper
  length.
Expand and test constant names.

* Purge exec flag from constants.py
* Define the maximum number of contacts per replacement cache.
Test and refactor getRefreshList.

* Be deterministic; do not use randomized IDs.
* Drop _randomIDInBucketRange as it is no longer used.
* Use a list comprehension for simplicity.
* Avoid invoking time.time() many times. :P
* Optimization: do not enter loop if force flag is set.
* Drop unused import.
Drop addContact from TreeRoutingTable.

* Its proper implementation is contested.
* It references undefined names ("addErrback").
* The class itself is nowhere used in the code.
* It is very difficult to test, as it entails the network.
Delegate splitting to the KBucket.

* A KBucket should handle the details of its splitting. This
  will enable using different subclasses of KBucket with the
  RoutingTable. It is also necessary to write thread-safe code.
* Test kbucket.splitKBucket.
Add and test MemKBucket.

* Test MemKbucket initialization.
* Test MemKbucket against the superclass testsuite.
* Model and test the replacement cache as a deque.
* Test cache-splitting.
Protect access to KBucket attributes via an RLock.

* A Kbucket is now a thread-safe object.
Replace TreeRoutingTable by OptimizedTreeRoutingTable.

* Dump splitKBucket inside addContact.
* Some docstring fixes.
* Drop TreeRoutingTable from the testsuite.