docs: Copyright updated for 2013
+func: added MissingDependencyException

Added an exception class for when the functionality of an object
depends on a missing external software library.
reliability: graceful degradation in cheshire3.graph

Graph (RDF) handling sub-package degrades gracefully when missing
library dependencies.
reliability: graceful degradation in cheshire3.grid

Data grid sub-package degrades gracefully when missing library
dependencies.
reliability: graceful degradation in cheshire3.datamining

Data mining sub-package degrades gracefully when missing library
dependencies.
reliability: graceful degradation in cheshire3.lucene

Lucene sub-package degrades gracefully when missing library
dependencies.
+func: import all sub-packages to initiate on-init hooks

e.g. to add DocumentStreams, QueryStreams to base factories

Don't catch errors when importing. Each sub-package is responsible for
degrading gracefully in absence of dependencies (i.e. don't fail until
missing functionality is explicitly called).
style: fixed str and repr for C3Exceptions
reliability: catch MissingDependencyException in `cheshire3-load`