bug 263:

- encode/decode target triple and dependent libraries
bug 401:
- fix encoding/decoding of FP values to be little-endian only
bug 402:
- initial (compatible) cut at 24-bit types instead of 32-bit
- reduce size of block headers by 50%
Other:
- cleanup Writer by consolidating to one compilation unit, rem. other files
- use a std::vector instead of std::deque so the buffer can be allocated
  in multiples of 64KByte chunks rather than in multiples of some smaller
  (default) number.

llvm-svn: 15210