Add higher level pathspec API

Right now, setting up a pathspec to be parsed and processed
requires several data structures and a couple of API calls.  This
adds a new high level data structure that contains all the items
that you'll need and high-level APIs that do all of the setup and
all of the teardown.  This will make it easier to use pathspecs
in various places with less repeated code.

src/pathspec.c

@@ -166,3 +166,28 @@ bool git_pathspec_match_path(
 	return false;
 }
 
+
+int git_pathspec_context_init(
+	git_pathspec_context *ctxt, const git_strarray *paths)
+{
+	int error = 0;
+
+	memset(ctxt, 0, sizeof(*ctxt));
+
+	ctxt->prefix = git_pathspec_prefix(paths);
+
+	if ((error = git_pool_init(&ctxt->pool, 1, 0)) < 0 ||
+		(error = git_pathspec_init(&ctxt->pathspec, paths, &ctxt->pool)) < 0)
+		git_pathspec_context_free(ctxt);
+
+	return error;
+}
+
+void git_pathspec_context_free(
+	git_pathspec_context *ctxt)
+{
+	git__free(ctxt->prefix);
+	git_pathspec_free(&ctxt->pathspec);
+	git_pool_clear(&ctxt->pool);
+	memset(ctxt, 0, sizeof(*ctxt));
+}

src/pathspec.h

@@ -37,4 +37,18 @@ extern bool git_pathspec_match_path(
 	bool casefold,
 	const char **matched_pathspec);
 
+/* easy pathspec setup */
+
+typedef struct {
+	char *prefix;
+	git_vector pathspec;
+	git_pool pool;
+} git_pathspec_context;
+
+extern int git_pathspec_context_init(
+	git_pathspec_context *ctxt, const git_strarray *paths);
+
+extern void git_pathspec_context_free(
+	git_pathspec_context *ctxt);
+
 #endif