The majority of functions are named `from_something` (with an
underscore) instead of `fromsomething`.  Update the tag function for
consistency with the rest of the library.

The majority of functions are named `from_something` (with an
underscore) instead of `fromsomething`.  Update the index functions for
consistency with the rest of the library.

The majority of functions are named `from_something` (with an
underscore) instead of `fromsomething`.  Update the blob functions for
consistency with the rest of the library.

The only function that is named `issomething` (without underscore) was
`git_oid_iszero`.  Rename it to `git_oid_is_zero` for consistency with
the rest of the library.

Docurium seems to choke on this header because it can't see both
git_indexer_progress & git_indexer_progress_cb, let's add the include.

In libgit2 nomenclature, when we need to verb a direct object, we name
a function `git_directobject_verb`.  Thus, if we need to init an options
structure named `git_foo_options`, then the name of the function that
does that should be `git_foo_options_init`.

The previous names of `git_foo_init_options` is close - it _sounds_ as
if it's initializing the options of a `foo`, but in fact
`git_foo_options` is its own noun that should be respected.

Deprecate the old names; they'll now call directly to the new ones.

The trace logging callbacks should match the other callback naming
conventions, using the `_cb` suffix instead of a `_callback` suffix.

The credential callbacks should match the other callback naming
conventions, using the `_cb` suffix instead of a `_callback` suffix.