add version command to give dep's version

[jessfraz]

This makes it so we can do this:

$ ./dep version
dep version 0.0.0 3a8f368 linux/amd64

It also adds a Makefile for running with the specific flags to input the version into the command and/or cross-compile the binaries for various platforms which we will ultimately need if we decide to release this.

Now I am unsure what the standard Go team practices are for Makefiles but I have a feeling they are not exactly fans. I am though a huge fan of make.... so let the bikeshed begin hahaha

Also I added a help command to our Makefile so you can do this:

$ make help
build                          Builds a dynamic executable
clean                          Cleanup any build binaries
cross                          Builds the cross-compiled binaries, creating a clean directory structure (eg. GOOS/GOARCH/binary)
static                         Builds a static executable

[freeformz]

I suck at advanced Makefileing, but otherwise 👍 from me.

[adg]

Add a comment that describes what this does.

[jessfraz]

closing for now we can discuss other alternatives to my lord and savior make