* Added support for seek() and tell()
* Added filelike.join() for concatenating several files
into one file-like object
* Added filelike.slice() for accessing a portion of a file
* Added support for context-manager protocol
* Much better support for intermingled reads and writes
* Restructured the 'wrappers' module to provide a consistent
naming scheme
* all wrapper classes are now read-wise verbs, e.g.
Decrypt(f) will decrypt all reads from f, and encrypt
all writes.
* removed 'Cat' in favour of filelike.join
* Switched to new-style classes throughout