Always use what the old implementation called the "IO" allocation
scheme, allowing to move the content pointer past the initial
allocation. This is inexpensive and allows efficient shrinking.
Optimize xmlBufGrow, reusing shrunken memory as much as possible.
Simplify xmlBufAdd.
Make xmlBufBackToBuffer return an error on overflow.
Make "size" exclude the terminating NULL byte.
Always provide an initial size.
Reintroduce static buffers.
Remove xmlBufResize and several other functions.
Private functions were previously declared
- in header files in the root directory
- in public headers guarded with IN_LIBXML
- in libxml.h
- redundantly in source files that used them.
Consolidate all private header files in include/private.
