Made httplib_pthread_key_create global

doc/api/httplib_pthread_key_create.md

@@ -0,0 +1,29 @@
+# LibHTTP API Reference
+
+### `httplib_pthread_key_create( key, destructor );`
+
+### Parameters
+
+| Parameter | Type | Description |
+| :--- | :--- | :--- |
+|**`key`**|`pthread_key_t`|The key of the variable to set|
+|**`destructor`**|`void (*destructor)(void *)`|Pointer to destructor function to be called when the key is destroyed|
+
+### Return Value
+
+| Type | Description |
+| :--- | :--- |
+|`int`|Integer value with the result of the function|
+
+### Description
+
+The platform independent function `httplib_pthread_key_create()` creates a key to a memory area for thread specific data storage. The function returns **0** when successful and an error code if something went wrong. On systems which support it, the functionality is implemented as a direct call to `pthread_key_create()`. Otherwise own code is used to emulate the same behaviour.
+
+Please not that on systems which don't support the `pthread_key_create()` function natively that the `destructor` parameter is ignored. For multiplatform execution you should check that this will not cause problems regarding the functionality.
+
+### See Also
+
+* [`httplib_pthread_getspecific();`](httplib_pthread_getspecific.md)
+* [`httplib_pthread_key_delete();`](httplib_pthread_key_delete.md)
+* [`httplib_pthread_setspecific();`](httplib_pthread_setspecific.md)
+* [`httplib_pthread_self();`](httplib_pthread_self.md)