Add JSONP mode and captcha

JSONP mode is on by default. It will fetch main wiki pages in the
browser, without the server needing to make any requests. To turn it
off, add [feature_json] enabled = false to config.ini.

Captcha is off by default. It is a custom solution and is still
experimental at this stage. If you turn it on, please monitor the logs
to see how it goes! config.ini options are as follows:

[captcha]
enabled = true|false
log = true|false
ip_header = <header name set by your reverse proxy, like x-forwarded-for>

breezewiki.rkt

@@ -1,5 +1,7 @@
 #lang racket/base
-(require web-server/servlet-dispatch
+(require racket/splicing
+         web-server/servlet-dispatch
+         web-server/safety-limits
          "src/config.rkt"
          "src/dispatcher-tree.rkt"
          "src/reloadable.rkt")
@@ -9,6 +11,9 @@
     (reloadable-entry-point->procedure
      (make-reloadable-entry-point (quote varname) filename))))
 
+(require-reloadable "src/page-captcha.rkt" page-captcha)
+(require-reloadable "src/page-captcha.rkt" page-captcha-image)
+(require-reloadable "src/page-captcha.rkt" page-captcha-verify)
 (require-reloadable "src/page-category.rkt" page-category)
 (require-reloadable "src/page-global-search.rkt" page-global-search)
 (require-reloadable "src/page-home.rkt" page-home)
@@ -22,7 +27,9 @@
 (require-reloadable "src/page-static-archive.rkt" page-static-archive)
 (require-reloadable "src/page-subdomain.rkt" subdomain-dispatcher)
 (require-reloadable "src/page-wiki.rkt" page-wiki)
+(require-reloadable "src/page-wiki.rkt" page-wiki-with-data)
 (require-reloadable "src/page-wiki-offline.rkt" page-wiki-offline)
+(require-reloadable "src/page-wiki-jsonp.rkt" page-wiki-jsonp)
 (require-reloadable "src/page-file.rkt" page-file)
 
 (reload!)
@@ -34,10 +41,14 @@
                  (if (config-true? 'debug) "127.0.0.1" #f)
                  (config-get 'bind_host))
    #:port (string->number (config-get 'port))
+   #:safety-limits (make-safety-limits #:max-request-body-length (* 8 1024 1024))
    (λ (quit)
      (channel-put ch (lambda () (semaphore-post quit)))
      (dispatcher-tree
       ; order of these does not matter
+      page-captcha
+      page-captcha-image
+      page-captcha-verify
       page-category
       page-global-search
       page-home
@@ -48,7 +59,9 @@
       page-set-user-settings
       page-static-archive
       page-wiki
+      page-wiki-with-data
       page-wiki-offline
+      page-wiki-jsonp
       page-file
       redirect-wiki-home
       static-dispatcher