Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>

`git_reference_rename` now takes a `force` flag

A bunch of redundant methods have been removed from the external API.

- All the reference/tag creation methods with `_f` are gone. The force
flag is now passed as an argument to the normal create methods.

- All the different commit creation methods are gone; commit creation
now always requires a `git_commit` pointer for parents and a `git_tree`
pointer for tree, to ensure that corrupted commits cannot be generated.

- All the different tag creation methods are gone; tag creation now
always requires a `git_object` pointer to ensure that tags are not
created to inexisting objects.

Fix all the missmatched arguments in the docs

Same name as `git_config_foreach`

Internal methods are static and without the git prefix.
'Force' methods have a `_f` prefix to match the other 'force' methods.

Signed-off-by: Carlos Martín Nieto <cmn@elego.de>

Add internal reference create and rename functions which take a force
parameter, telling them to overwrite an existing reference if it
exists.

These functions try to update the reference if it's of the same type
as the one it's going to be replaced by. Otherwise the old reference
becomes invalid.

Signed-off-by: Carlos Martín Nieto <cmn@elego.de>

List all the references in the repository, calling a custom
callback for each one.

The listed references may be filtered by type, or using
a bitwise OR of several types. Use the magic value
`GIT_REF_LISTALL` to obtain all references, including
packed ones.

The `callback` function will be called for each of the references
in the repository, and will receive the name of the reference and
the `payload` value passed to this method.

Lists all the references in a repository. Listing may be filtered by
reference type.

This should applease Lord Clem.