Rename API to follow a new naming convention:
* XCB_CONSTANTS_UPPERCASE_WITH_UNDERSCORES
* xcb_functions_lowercase_with_underscores
* xcb_types_lowercase_with_underscores_and_suffix_t
* expand all abbreviations like "req", "rep", and "iter"

Word boundaries for the names in the protocol descriptions fall:
* Wherever the protocol descriptions already have an underscore
* Between a lowercase letter and a subsequent uppercase letter
* Before the last uppercase letter in a string of uppercase letters followed
  by a lowercase letter (such as in LSBFirst between LSB and First)
* Before and after a string of digits (with exceptions for sized types like
  xcb_char2b_t and xcb_glx_float32_t to match the stdint.h convention)

Also fix up some particular naming issues:
* Rename shape_op and shape_kind to drop the "shape_" prefix, since otherwise
  these types end up as xcb_shape_shape_{op,kind}_t.
* Remove leading underscores from enums in the GLX protocol description,
  previously needed to ensure a word separator, but now redundant.

This renaming breaks code written for the previous API naming convention.  The
scripts in XCB's tools directory will convert code written for the old API to
use the new API; they work well enough that we used them to convert the
non-program-generated code in XCB, and when run on the old program-generated
code, they almost exactly reproduce the new program-generated code (modulo
whitespace and bugs in the old code generator).

Authors: Vincent Torri, Thomas Hunger, Josh Triplett