style: fixed coding style in the header files consts.h and args.h. thanks Tatsuhiko Kubo for the report in #392.
doc: improved the wording of the documentation for ngx.req.clear_header() to prevent ambiguity. thanks Christophe-Marie Duquesne for the report in #393.
tests: improved the test cases for the ngx.header API a little bit.
feature: added pure C API function for FFI-based implementation of reading ngx.header.HEADER.
optimize: reading ngx.header.HEADER: eliminated dynamic allocations and data copying when there is no need to ransform "_" to "-" in the header name.