improve install from source

* Idempotent clone_and_build.sh does everything
* Add documentation for how to build in Docker

Had to sacrificy go generate because stringer apparently can't handle
vendor directory used by go dep, fails with error
on go generate rpc/frame_layer.go

refs #37

clone_and_build.sh

@@ -0,0 +1,45 @@
+#!/bin/sh -e
+
+bold=$(tput bold)
+normal=$(tput sgr0)
+
+step() {
+    echo "${bold}$1${normal}"
+}
+
+if [ -z "$GOPATH" ]; then
+    step "Make sure you have your GOPATH configured correctly" 1>&2
+    exit 1
+fi
+
+step "Checkout sources to \$GOPATH/github.com/zrepl/zrepl"
+CHECKOUTPATH="${GOPATH}/src/github.com/zrepl/zrepl"
+if [ -e "$CHECKOUTPATH" ]; then
+    echo "${CHECKOUTPATH} already exists"
+    if [ ! -d "$CHECKOUTPATH" ]; then
+        echo "${CHECKOUTPATH} is not a directory, aborting" 1>&2
+    else
+        cd "$CHECKOUTPATH"
+    fi
+else
+    mkdir -p "$GOPATH/src/github.com/zrepl"
+    cd "$GOPATH/src/github.com/zrepl"
+    git clone https://github.com/zrepl/zrepl.git
+    cd zrepl
+fi
+
+step "Install build depdencies using 'go get' to \$GOPATH/bin"
+go get -u golang.org/x/tools/cmd/stringer
+go get -u github.com/golang/dep/cmd/dep
+if ! type stringer || ! type dep; then
+    echo "Installed dependencies but can't find them in \$PATH, adjust it to contain \$GOPATH/bin" 1>&2
+    exit 1
+fi
+
+step "Fetching dependencies using 'dep ensure'"
+dep ensure
+
+step "Making release"
+make release
+
+step "Release artifacts are available in $(pwd)/artifacts"