Introduce default github build target

All plugins are expected to have a main build target
having the same name as the plugin's directory.

Introduce the 'github' plugin which is the main node
of the dependency of all other targets, including the one
responsible for extracting the plugin's version into a version
file.

Change-Id: I9fb3694e5fb2c4cbf0455d54281ee2677429d16f

BUILD

diff --git a/BUILD b/BUILD
index 501159f..41bb112 100644
--- a/BUILD
+++ b/BUILD
@@ -1,3 +1,16 @@
+load("//tools/bzl:genrule2.bzl", "genrule2")
+
+genrule(
+    name = "github",
+    srcs = [
+        ":github-plugin",
+        ":github-plugin-version",
+        ":github-oauth",
+    ],
+    outs = ["github.zip"],
+    cmd = "zip -o $@ $(SRCS)",
+)
+
 genrule(
     name = "github-oauth",
     srcs = ["//plugins/github/github-oauth:github-oauth_deploy.jar"],
@@ -5,6 +18,13 @@
     cmd = "cp $< $@",
 )
 
+genrule2(
+    name = "github-plugin-version",
+    srcs = [":github-plugin"],
+    outs = ["github-plugin.jar-version"],
+    cmd = "jar xvf $< META-INF/MANIFEST.MF; cat META-INF/MANIFEST.MF | grep Implementation-Version | cut -d ':' -f 2 | xargs > $@",
+)
+
 genrule(
     name = "github-plugin",
     srcs = ["//plugins/github/github-plugin"],