Refactor Mongoose documentation

PUBLISHED_FROM=e9a4e5c7b4a1d03b93a2a79e29de19e60e919929

docs/http/cgi.md

@@ -0,0 +1,31 @@
+---
+title: CGI
+---
+
+[CGI](https://en.wikipedia.org/wiki/Common_Gateway_Interface)
+is a simple mechanism to generate dynamic content.
+In order to use CGI, call `mg_serve_http()` function and use
+`.cgi` file extension for the CGI files. To be more precise,
+all files that match `cgi_file_pattern` setting in the
+`struct mg_serve_http_opts` are treated as CGI.
+If `cgi_file_pattern` is NULL, `**.cgi$|**.php$` is used.
+
+If Mongoose recognises a file as CGI, it executes it, and sends the output
+back to the client. Therefore,
+CGI file must be executable. Mongoose honours the shebang line - see
+http://en.wikipedia.org/wiki/Shebang_(Unix).
+
+For example, if both PHP and Perl CGIs are used, then
+``#!/path/to/php-cgi.exe` and ``#!/path/to/perl.exe` must be the first lines
+of the respective CGI scripts.
+
+It is possible to hardcode the path to the CGI interpreter for all
+CGI scripts and disregard the shebang line. To do that, set the
+`cgi_interpreter` setting in the `struct mg_serve_http_opts`.
+
+NOTE: PHP scripts must use `php-cgi.exe` as CGI interpreter, not `php.exe`.
+Example:
+
+```c
+  opts.cgi_interpreter = "C:\\ruby\\ruby.exe";
+```