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.

Konsus/libxml,improvisio-software/libxmljs,sergeche/libxmljs,gagern/libxmljs,gagern/libxmljs,rchipka/libxmljs,Visya/libxmljs,Konsus/libxml,libxmljs/libxmljs,hildjj/libxmljs,rc0x03/libxmljs,improvisio-software/libxmljs,polotek/libxmljs,rc0x03/libxmljs,hildjj/libxmljs,rchipka/libxmljs,Visya/libxmljs,rchipka/libxmljs,polotek/libxmljs,improvisio-software/libxmljs,Konsus/libxml,sergeche/libxmljs,polotek/libxmljs,libxmljs/libxmljs,Visya/libxmljs,hildjj/libxmljs,sergeche/libxmljs,libxmljs/libxmljs,gagern/libxmljs,rc0x03/libxmljs