Refactor; Add CHashmap for better concurrency

Currently using `DepGraph::grouped_resolve` in order to ease into naive
parallel service startup, also changed the way things are done inside
ServiceGraph, and added commented out code for rayon integration
(currently rayon is having all kinds of low-level issues).
2 jobs for dependencies in 4 minutes and 17 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
failed #8160
allowed to fail
build:linux:cargo

00:03:08

passed #8161
build:redox:cargo

00:04:16

 
Name Stage Failure
failed
build:linux:cargo Build

error: aborting due to 6 previous errors

For more information about this error, try `rustc --explain E0308`.
error: Could not compile `init`.

Caused by:
process didn't exit successfully: `rustc --edition=2018 --crate-name init src/main.rs --color never --crate-type bin --emit=dep-info,link -C debuginfo=2 -C metadata=e41deb71e0e9e9a7 -C extra-filename=-e41deb71e0e9e9a7 --out-dir /builds/redox-os/init/target/debug/deps -C incremental=/builds/redox-os/init/target/debug/incremental -L dependency=/builds/redox-os/init/target/debug/deps --extern chashmap=/builds/redox-os/init/target/debug/deps/libchashmap-0cd286b7e2a954e9.rlib --extern failure=/builds/redox-os/init/target/debug/deps/libfailure-a6721c5cdc6ff1af.rlib --extern generational_arena=/builds/redox-os/init/target/debug/deps/libgenerational_arena-61531e7242402ce6.rlib --extern log=/builds/redox-os/init/target/debug/deps/liblog-f7a6d80908936a04.rlib --extern syscall=/builds/redox-os/init/target/debug/deps/libsyscall-4b586bf24a6997c0.rlib --extern serde=/builds/redox-os/init/target/debug/deps/libserde-19c7db8fb3d65002.rlib --extern serde_derive=/builds/redox-os/init/target/debug/deps/libserde_derive-97ad4e52d032fce6.so --extern simple_logger=/builds/redox-os/init/target/debug/deps/libsimple_logger-134e4bef04d8deca.rlib --extern toml=/builds/redox-os/init/target/debug/deps/libtoml-06cc838a4777a2b7.rlib -L native=/builds/redox-os/init/target/debug/build/backtrace-sys-610efb92c11b858c/out` (exit code: 1)
ERROR: Job failed: exit code 1