doc: add documentation to all the public structs and enumscmn/doc-all

This makes them show up in the reference, even if the text itself isn't
the most descriptive.

These have been found with

    grep -Przon '\n\ntypedef struct.*?\{' -- include
    grep -Przon '\n\ntypedef enum.*?\{' -- include

1 files changed, 6 insertions, 0 deletions

diff --git a/include/git2/repository.h b/include/git2/repository.h
index 268782648..124aa67e6 100644
--- a/include/git2/repository.h
+++ b/include/git2/repository.h
@@ -661,6 +661,12 @@ GIT_EXTERN(int) git_repository_detach_head(
 	const git_signature *signature,
 	const char *reflog_message);
 
+/**
+ * Repository state
+ *
+ * These values represent possible states for the repository to be in,
+ * based on the current operation which is ongoing.
+ */
 typedef enum {
 	GIT_REPOSITORY_STATE_NONE,
 	GIT_REPOSITORY_STATE_MERGE,