Add robby-api-url customization variable.

Put the base API url in a customization variable, instead of hard-coding
it. This should let users use alternate OpenAI compatible providers.

Fixes #1.

README.org

@@ -34,6 +34,8 @@ builder to create custom commands without having to write code.
       - [[#built-in-action-functions][Built-in Action Functions]]
       - [[#built-in-grounding-functions][Built-in Grounding Functions]]
 - [[#customization][Customization]]
+      - [[#openai-url][OpenAI URL]]
+      - [[#api-options][API Options]]
 - [[#animated-gifs][Animated Gifs]]
 
 * Requirements
@@ -468,7 +470,12 @@ Replace =%= with =%%= in TEXT to avoid format string errors calling ~message~.
 *** ~robby-remove-trailing-end-of-line~
 Remove the end of line character at the very end of a string if present.
 * Customization
-Use ~customize-group~ | ~robby~ to see the various customization options. Robby will validate values as appropriate, for example ~robby-chat-temperature~ values must be between =0.0= and =2.0=. 
+Use ~customize-group~ | ~robby~ to see the various customization options. Robby will validate values as appropriate, for example ~robby-chat-temperature~ values must be between =0.0= and =2.0=.
+
+** OpenAI URL
+Customize the ~robby-chat-api~ variable to use a different OpenAI compatible provider. By default it is set to =https://api.openai.com/v1/chat/completions=. 
+
+** API Options
 
 The ~robby-chat-api~ customization group species the OpenAI API options. Here are
 a few important ones:

robby-customization.el

@@ -88,6 +88,11 @@ It should include a `%s' placeholder for the spinner."
   :type 'string
   :group 'robby)
 
+(defcustom robby-api-url "https://api.openai.com/v1/chat/completions"
+  "URL to use for OpenAI API requests."
+  :type 'string
+  :group 'robby)
+
 ;;; chat api options
 (defgroup robby-chat-api nil
   "Options to pass to the chat API."

robby-request.el

@@ -13,12 +13,10 @@
 (require 'url-vars)
 
 (require 'robby-api-key)
+(require 'robby-customization)
 (require 'robby-logging)
 (require 'robby-utils)
 
-;;; constants
-(defconst robby--request-url "https://api.openai.com/v1/chat/completions")
-
 ;;; util functions
 (defun robby--request-parse-error-data (data)
   "Get error from response DATA."
@@ -102,7 +100,7 @@ STREAMP is non-nil if the response is a stream."
                           "curl"
                           proc-buffer
                           "curl"
-                          robby--request-url
+                          robby-api-url
                           curl-options)
                  (error (funcall on-error err)))))
     (let ((remaining "")
@@ -163,7 +161,7 @@ ON-ERROR is the callback for when an error is received."
          (message-log-max nil))
     (robby--log (format "#url-retrieve request JSON payload:\n%s\n" url-request-data))
     (url-retrieve
-     robby--request-url
+     robby-api-url
      (lambda (_status)
        (goto-char (point-min))
        (re-search-forward "^{")