Document git_fetch_options struct and fix typo.

git_fetch_options was missing from the API docs because it lacked a
documentation comment above the struct declaration.
I used the git_checkout_options docstring as a template.

Also fixes a typo in git_remote_prune_refs (remote, not reamote).

include/git2/remote.h

@@ -511,6 +511,14 @@ typedef enum {
 	GIT_REMOTE_DOWNLOAD_TAGS_ALL,
 } git_remote_autotag_option_t;
 
+/**
+ * Fetch options structure.
+ *
+ * Zero out for defaults.  Initialize with `GIT_FETCH_OPTIONS_INIT` macro to
+ * correctly set the `version` field.  E.g.
+ *
+ *		git_fetch_options opts = GIT_FETCH_OPTIONS_INIT;
+ */
 typedef struct {
 	int version;
 
@@ -739,7 +747,7 @@ GIT_EXTERN(int) git_remote_prune_refs(const git_remote *remote);
  * stored here for further processing by the caller. Always free this
  * strarray on successful return.
  * @param repo the repository in which to rename
- * @param name the current name of the reamote
+ * @param name the current name of the remote
  * @param new_name the new name the remote should bear
  * @return 0, GIT_EINVALIDSPEC, GIT_EEXISTS or an error code
  */