Add Haiku support

[sikmir]

Ref. termios.h

[dcuddeback]

@sikmir Thanks for sending in the patch, and sorry for the long delay. I've been on Haitus for a while.

I was working on landing this today. My progress is in this commit: 3d62fc7. I made a couple changes based on the header files:

• Redefined tcflag_t as u32. It's typedef'd as __haiku_uint32 in termios.h. I think u32
  matches the intended use of that type.
• I provided an implementation for cfsetspeed(), because that seems to be missing in Haiku.
  Without it, anything that attempts to use cfsetspeed() will fail to compile.

However, I wasn't able to compile it on Haiku. Cargo crashes with a segfault inside openssl. Would you be able to verify that cargo build and cargo test run successfully on Haiku using the feature/haiku branch?

Also, any idea what I might be doing wrong to get Rust running on Haiku? I installed Rust with pkgman install rust_bin. I tried the beta release as well as the latest nightly. I'm not familiar with Haiku.

[dcuddeback]

@sikmir Closing in favor of #26, which has the changes I made. I'm looking for help getting Rust running on Haiku so that I can test it. If you can help, please see #26.