Switch to exclusively using global ctx

Drop the context parameter from the following functions (and all static
helpers used by them) and use the global context instead:

* cgit_print_http_headers()
* cgit_print_docstart()
* cgit_print_pageheader()

Remove context parameter from all commands

Drop the context parameter from the following functions (and all static
helpers used by them) and use the global context instead:

* cgit_get_cmd()
* All cgit command functions.
* cgit_clone_info()
* cgit_clone_objects()
* cgit_clone_head()
* cgit_print_plain()
* cgit_show_stats()

In initialization routines, use the global context variable instead of
passing a pointer around locally.

Remove callback data parameter for cache slots

This is no longer needed since the context is always read from the
global context variable.

Signed-off-by: Lukas Fleischer <cgit@cryptocrack.de>

ui-atom.c

@@ -108,7 +108,7 @@ void cgit_print_atom(char *tip, char *path, int max_count)
 	host = cgit_hosturl();
 	ctx.page.mimetype = "text/xml";
 	ctx.page.charset = "utf-8";
-	cgit_print_http_headers(&ctx);
+	cgit_print_http_headers();
 	html("<feed xmlns='http://www.w3.org/2005/Atom'>\n");
 	html("<title>");
 	html_txt(ctx.repo->name);