Move source code for xmllint shell to shell.c and move it from the
libxml2 library to the xmllint executable.
Also allow shell to run without XPath and debug modules.
Add stubs for old shell API functions in legacy build mode.
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.