Tweak interface to allow reading from an input stream (as well as buffer).
Fix typo.
Add streaming output.
Document the new streaming interface.
Add seek-bunzip executable.
Add ability to read 'multistream' bzip2 files.

"Multistream" files are just multiple independent bzip2-compressed files
concatenated together.
Add bzip-table indexing functionality; update docs and tests.
Update version #.