feature: now we save the original pattern string pointer value into our ngx_http_lua_regex_t struct, to help runtime regex profiling and debugging.
fixed the wrong return type of the ngx_http_lua_ffi_req_start_time function in the previous commit.
feature: added pure C API function ngx_http_lua_ffi_time for FFI-based implementations of ngx.time().
renamed ngx_http_lua_ffi_ngx_now to ngx_http_lua_ffi_now.
optimize: use lua_pushinteger instead of lua_pushnumber in ngx_http_lua_ngx_time().
the "int" return type of ngx_http_lua_ffi_time might lead to data loss. thanks itpp16 for the report.
Revert "optimize: use lua_pushinteger instead of lua_pushnumber in ngx_http_lua_ngx_time()."

The lua_Integer type might lead to data loss.

This reverts commit e9b8563c32d4ef0510c5a6012defba15aaf9c9b5.
feature: added pure C API functions for FFI-based implementations of ngx.req.get_method().
feature: added pure C API function for FFI-based implementations of ngx.req.set_method().
feature: added a pure C API function for FFI implementations of shdict:flush_all().
feature: added a pure C API function for FFI-based implementations of ngx.req.set_header() (single-value only) and ngx.req.clear_header().
bugfix: ngx.req.set_method(): we incorrectly modified r->method when the method ID was wrong.
resolved merge conflicts.
added assertions to the coroutine scheduler to ensure that we do not pop or push the wrong number of stack slots for yielded coroutines.
use ngx_http_lua_assert() instead of plain assert() across the code base.
doc: moved important sections to the front. thanks Pierre-Yves Gérardy for the patch in #371.
doc: moved the "Directives" and "Nginx API for Lua" sections to the end because they are too long and kinda boring :) thanks Pierre-Yves Gérardy for the patch in #371.
doc: markdown format: inlined the TOC for the long sections "Directives" and "Nginx API for Lua" as per Pierre-Yves Gérardy's suggestion in #370.
bumped version to 0.9.8.
doc: documented the values can be passed to the timer callback function.