Add some keywords to the main agb crates (#802)

Might be nice to have these keywords show up in crates.io

- [x] no changelog update needed

agb-fixnum/Cargo.toml

@@ -5,6 +5,7 @@ edition = "2021"
 license = "MPL-2.0"
 description = "Library for abstracting over fixed precision numbers. Designed for use with the agb library for the Game Boy Advance"
 repository = "https://github.com/agbrs/agb"
+keywords = ["no-std", "no-std::no-alloc"]
 
 [dependencies]
 agb_macros = { version = "0.21.1", path = "../agb-macros" }

agb-hashmap/Cargo.toml

@@ -6,6 +6,7 @@ license = "MPL-2.0"
 description = "A simple no_std hashmap implementation intended for use in the `agb` library"
 repository = "https://github.com/agbrs/agb"
 exclude = ["/benches"]
+keywords = ["no-std", "data-structures"]
 
 [features]
 allocator_api = []

agb/Cargo.toml

@@ -8,6 +8,7 @@ license = "MPL-2.0"
 repository = "https://github.com/agbrs/agb"
 homepage = "https://agbrs.dev"
 exclude = ["/tests", "/examples"]
+keywords = ["game-engines", "embedded"]
 
 [features]
 default = ["backtrace", "testing"]