Mark some symbols to be deprecated #minor (#698)

This change introduces the file deprecated.go, which contains any
constants, functions, and types that are slated to be deprecated in the
next major release.

These symbols are deprecated because they refer to old spellings in
pre-1.0 libgit2. This also makes the build be done with the
`-DDEPRECATE_HARD` flag to avoid regressions.

This, together with
[gorelease](https://godoc.org/golang.org/x/exp/cmd/gorelease)[1] should
make releases safer going forward.

1: More information about how that works at
   https://go.googlesource.com/exp/+/refs/heads/master/apidiff/README.md

1 files changed, 10 insertions, 10 deletions

diff --git a/stash.go b/stash.go
index bba9bad..7e0ed8f 100644
--- a/stash.go
+++ b/stash.go
@@ -140,7 +140,7 @@ func stashApplyProgressCb(progress C.git_stash_apply_progress_t, handle unsafe.P
 // StashApplyOptions represents options to control the apply operation.
 type StashApplyOptions struct {
 	Flags            StashApplyFlag
-	CheckoutOptions  CheckoutOpts               // options to use when writing files to the working directory
+	CheckoutOptions  CheckoutOptions            // options to use when writing files to the working directory
 	ProgressCallback StashApplyProgressCallback // optional callback to notify the consumer of application progress
 }
 
@@ -173,7 +173,7 @@ func (opts *StashApplyOptions) toC() (
 			version: C.GIT_STASH_APPLY_OPTIONS_VERSION,
 			flags:   C.uint32_t(opts.Flags),
 		}
-		populateCheckoutOpts(&optsC.checkout_options, &opts.CheckoutOptions)
+		populateCheckoutOptions(&optsC.checkout_options, &opts.CheckoutOptions)
 		if opts.ProgressCallback != nil {
 			C._go_git_setup_stash_apply_progress_callbacks(optsC)
 			optsC.progress_payload = pointerHandles.Track(progressData)
@@ -191,21 +191,21 @@ func untrackStashApplyOptionsCallback(optsC *C.git_stash_apply_options) {
 
 func freeStashApplyOptions(optsC *C.git_stash_apply_options) {
 	if optsC != nil {
-		freeCheckoutOpts(&optsC.checkout_options)
+		freeCheckoutOptions(&optsC.checkout_options)
 	}
 }
 
 // Apply applies a single stashed state from the stash list.
 //
 // If local changes in the working directory conflict with changes in the
-// stash then ErrConflict will be returned.  In this case, the index
+// stash then ErrorCodeConflict will be returned.  In this case, the index
 // will always remain unmodified and all files in the working directory will
 // remain unmodified.  However, if you are restoring untracked files or
 // ignored files and there is a conflict when applying the modified files,
 // then those files will remain in the working directory.
 //
 // If passing the StashApplyReinstateIndex flag and there would be conflicts
-// when reinstating the index, the function will return ErrConflict
+// when reinstating the index, the function will return ErrorCodeConflict
 // and both the working directory and index will be left unmodified.
 //
 // Note that a minimum checkout strategy of 'CheckoutSafe' is implied.
@@ -213,12 +213,12 @@ func freeStashApplyOptions(optsC *C.git_stash_apply_options) {
 // 'index' is the position within the stash list. 0 points to the most
 // recent stashed state.
 //
-// Returns error code ErrNotFound if there's no stashed state for the given
-// index, error code ErrConflict if local changes in the working directory
+// Returns error code ErrorCodeNotFound if there's no stashed state for the given
+// index, error code ErrorCodeConflict if local changes in the working directory
 // conflict with changes in the stash, the user returned error from the
 // StashApplyProgressCallback, if any, or other error code.
 //
-// Error codes can be interogated with IsErrorCode(err, ErrNotFound).
+// Error codes can be interogated with IsErrorCode(err, ErrorCodeNotFound).
 func (c *StashCollection) Apply(index int, opts StashApplyOptions) error {
 	optsC, progressData := opts.toC()
 	defer untrackStashApplyOptionsCallback(optsC)
@@ -298,7 +298,7 @@ func (c *StashCollection) Foreach(callback StashCallback) error {
 // 'index' is the position within the stash list. 0 points
 // to the most recent stashed state.
 //
-// Returns error code ErrNotFound if there's no stashed
+// Returns error code ErrorCodeNotFound if there's no stashed
 // state for the given index.
 func (c *StashCollection) Drop(index int) error {
 	runtime.LockOSThread()
@@ -320,7 +320,7 @@ func (c *StashCollection) Drop(index int) error {
 //
 // 'opts' controls how stashes are applied.
 //
-// Returns error code ErrNotFound if there's no stashed
+// Returns error code ErrorCodeNotFound if there's no stashed
 // state for the given index.
 func (c *StashCollection) Pop(index int, opts StashApplyOptions) error {
 	optsC, progressData := opts.toC()