convert LXJS_GET_PARSER_FROM_CONTEXT into a function
convert LXJS_GET_PARSER_FROM_CONTEXT into a function

Macros are inconsistent across platforms and bad practice unless no
other way is available. The uses of this macro are fine with a function
call.

CodeFridge/libxmljs_mem,CodeFridge/libxmljs_mem,CodeFridge/libxmljs_mem