Use a submodule for libgit2

This makes building the static version easier as we know where the repo
is and that it's has a known-good version.

Author: carlosmn

.gitmodules

@@ -0,0 +1,6 @@
+[submodule "libgit2"]
+	path = libgit2
+	url = ./vendor/libgit2
+[submodule "vendor/libgit2"]
+	path = vendor/libgit2
+	url = https://github.com/libgit2/libgit2

Makefile

@@ -3,11 +3,6 @@ default: test
 build-libgit2:
 	./script/build-libgit2-static.sh
 
-update-libgit2:
-	cd vendor/libgit2 && \
-	git fetch origin development && \
-	git checkout -qf FETCH_HEAD
-
 test: build-libgit2
 	./script/with-static.sh go test ./...
 

README.md

@@ -6,7 +6,12 @@ Go bindings for [libgit2](http://libgit2.github.com/). These bindings are for to
 Installing
 ----------
 
-Just `go get github.com/libgit2/git2go`. You'll need to have top-of-the-branch libgit2 from development installed in your system and available via `pkg-config`. These bindings are in sync with the top of `development`.
+This project needs libgit2, which is written in C so we need to take an extra step. Run `go get github.com/libgit2/git2go` and go to your `$GOROOT/src/github.com/libgt2/git2go` dir. From there, we need to build the C code and put it into the resulting go binary.
+
+    git submodule update --init
+	make install
+
+will compile libgit2, build it statically into git2go and install the resulting object file where your Go project can use it.
 
 License
 -------

script/build-libgit2-static.sh

@@ -4,11 +4,6 @@ set -ex
 
 VENDORED_PATH=vendor/libgit2
 
-# Make sure we have the latest libgit2
-if [ ! -d $VENDORED_PATH ]; then
-    git clone --depth 1 --single-branch git://github.com/libgit2/libgit2 $VENDORED_PATH
-fi
-
 cd $VENDORED_PATH
 
 cmake -DTHREADSAFE=ON \