refactor: many improvements to the NGINX module config script.

[thibaultcha]

This is a major refactor of the config script of this module.

• The script is now compatible for both ngx_http_lua and ngx_stream_lua
• ngx_sream_lua can now be compiled as a dynamic module
• The script is able to skip many steps if another Lua module has previously been configured, which avoids many redundant operations and compilation flags
• The script now automatically detects source files in the src/ directory
• Large refactor for improved maintainability
• Force pcre_version symbol
  • Fixed an issue on Darwin for static PCRE builds
  • Require the symbol to be defined for linking
  • Smarter linker flags detection depending on platform
• Require LuaJIT with FFI
  • Fixed an issue on Darwin which prevented the test from ever succeeding; it now statically links before running to avoid an issue with the .dylib location
• Added a vi modeline

I hereby granted the copyright of the changes in this pull request to the authors of this lua-nginx-module project.

[mergify[bot]]

This pull request is now in conflict :(