Reduced obfuslate to 1747 characters.
Factored out a variable. Rearranged alphabet up top.
Added a smaller version that supports BTYPE=11 only (dynamic Huffman
code blocks).

This is the most commonly used block type. To generate a file using
BTYPE=00 you need to code it your self, i.e., gzip's lowest
compression setting is 1. BTYPE=01 is also not very common as you
usually get more bang for your buck using BTYPE=11.