Eliminate .bzl files, support arbitrary target plats, and lightly refactor for other build tools

[acmcarther]

I'm looking to make good on the idea of special "designated platforms", since I think its a viable strategy. This opens the door to a one size fits all BUILD file generation process, whose end user customization is facilitated by Buildozer.

This change implies that bzl files will be no more (as they won't be useful).

It adds a "--targets" flag to cargo-raze that synthesizes build rules for each target platform with the exact required dependencies.

It will also see the removal of the bazel rules for cargo-raze, as there will no longer be an intermediate process -- cargo-raze will deliver ready-to-use BUILD files.

[acmcarther]

An example invocation:

cargo-raze raze //hello_cargo_library --targets="x86_64-unknown-linux-gnu,i686-pc-windows-msvc" 

[lilianmoraru]

That's some awesome work!
I love the decision to use a template engine, especially a good one(IMO).

I was not planning to say this but since I am looking at the template, I see one issue.
While I personally don't care for Windows development, cmd is not very cross-platformy(not a word, I know 😄 ).

[acmcarther]

I appreciate the comment (and the suggestion regd genrule.cmd):

I'm still doing a lot of investigative work here to try to get to somewhere where common crates are buildable. Unfortunately, that means basically everything but the kitchen sink, since most everything depends on openssl... which is a very painful dep to automatically handle.

I'll try to keep more public updates, and I'm currently working on more documentation around design decisions (and alternatives considered). Thanks again for looking!