A batch of updates to get to xgboost 2.0.3

[montanalow]

trafficstars

• builds with xgboost v2.0.3
• expose cuda support as a feature
• some additional OS X (openmp) compatibility for homebrew
• move upstream to dmlc/xgboost
• fix cargo dependencies for git submodules
• update cargo dependencies
• update DMatrix uri loading format for 2.0 compat
• fix cargo clippy lints
  • static lifetimes are no longer required
• fix dmatrix slicing out of bounds segfault
• cargo fmt (rustfmt.toml to minimize changes where possible)

Needs detailed review:

• From csr does not pass tests, but from csc is easier for me to reason about:
  • https://github.com/davechallis/rust-xgboost/compare/master...postgresml:rust-xgboost:master#diff-5395154ef0eed4cb8417ab3dfac078a8e79d26947d6967aa0800ad0460d81b1aR67

[davechallis]

@montanalow Thanks for this, looks good on quick read through! I'll spend a bit of time reviewing in detail shortly (just dealing with a bit of a backlog after xmas...).

[montanalow]

Code changes mostly look good I think.

I'm having some trouble building xgboost-sys after the changes though, so still investigating that. I get the errors:

error[E0412]: cannot find type `_Tp` in this scope
   --> /Users/dsc/src/rust-xgboost/xgboost-sys/target/debug/build/xgboost-sys-95c0101c1ac52cb0/out/bindings.rs:452:27
    |
452 |     pub static std_value: _Tp;
    |                           ^^^ not found in this scope

For more information about this error, try `rustc --explain E0412`.
error: could not compile `xgboost-sys` (lib) due to previous error

I'll carry on trying to find the cause though, possible I'm using an outdated llvm install.

This one took me a bit, but I think it's fixed by https://github.com/davechallis/rust-xgboost/pull/21/commits/0307a92960290bbe74b69cdeff2dd9090201f346