Do not generate colors phf map at compile time

phf_codegen is a pretty big dependency and colors will not change from build to build, so maybe it's better to keep the colors map as a "prebuilt" file? Something like this.

The source of the problem:

cssparser v0.24.1 (./rust-cssparser-0.24.1)                                         
├── cssparser-macros v0.3.4 (./rust-cssparser-0.24.1/macros)
│   ├── phf_codegen v0.7.24
│   │   ├── phf_generator v0.7.24
│   │   │   ├── phf_shared v0.7.24
│   │   │   │   └── siphasher v0.2.3
│   │   │   └── rand v0.6.5
│   │   │       ├── libc v0.2.48
│   │   │       ├── rand_chacha v0.1.1
│   │   │       │   └── rand_core v0.3.1
│   │   │       │       └── rand_core v0.4.0
│   │   │       │   [build-dependencies]
│   │   │       │   └── autocfg v0.1.2
│   │   │       ├── rand_core v0.4.0 (*)
│   │   │       ├── rand_hc v0.1.0
│   │   │       │   └── rand_core v0.3.1 (*)
│   │   │       ├── rand_isaac v0.1.1
│   │   │       │   └── rand_core v0.3.1 (*)
│   │   │       ├── rand_jitter v0.1.3
│   │   │       │   └── rand_core v0.4.0 (*)
│   │   │       ├── rand_os v0.1.2
│   │   │       │   ├── libc v0.2.48 (*)
│   │   │       │   └── rand_core v0.4.0 (*)
│   │   │       ├── rand_pcg v0.1.1
│   │   │       │   └── rand_core v0.3.1 (*)
│   │   │       │   [build-dependencies]
│   │   │       │   └── rustc_version v0.2.3
│   │   │       │       └── semver v0.9.0
│   │   │       │           └── semver-parser v0.7.0
│   │   │       └── rand_xorshift v0.1.1
│   │   │           └── rand_core v0.3.1 (*)
│   │   │       [build-dependencies]
│   │   │       └── autocfg v0.1.2 (*)
│   │   └── phf_shared v0.7.24 (*)

It's like 20 dependencies just to build a phf map, that never changes.

Start by locating the colors map generation in the cssparser-macros code and compare the proposed prebuilt-file approach with the linked svgtypes colors.rs. Check the dependency tree before and after; done means the colors map is kept in source form without requiring phf_codegen and its generator dependencies at compile time.