protoc-rust 1.4.0

protoc --rust_out=... available as API. protoc needs to be in $PATH, protoc-gen-run does not.
Documentation 
# API to generate .rs files

API to generate `.rs` files to be used e. g. [from build.rs](https://github.com/stepancheg/rust-protobuf/blob/master/protobuf-test/build.rs).

Example code:

```
extern crate protoc_rust;

protoc_rust::run(protoc_rust::Args {
    out_dir: "src/protos",
    input: &["protos/a.proto", "b.proto"],
    includes: &["protos"],
}).expect("protoc");
```

Note this API requires `protoc` command present in `$PATH`.
Although `protoc-gen-rust` command is not needed.