feat(spike): rover core build (#340)

* feat(spike): rover graph build

this PR introduces a TOML config format for specifying multiple
subgraphs to compose.

usage: rover graph build --services ./path/to/services.toml

This will attempt to compose your subgraph schemas. If it successfully composes,
it will print the composed CSDL.

If there are errors, they will be printed.

examples of both composing and non-composing inputs can be tested by running:

`cargo run -- graph build --services spike/composes.toml`

and

`cargo run -- graph build --services spike/errors.toml`

Cargo.toml

@@ -35,12 +35,13 @@ timber = { path = "./crates/timber" }
 anyhow = "1.0.38"
 atty = "0.2.14"
 ansi_term = "0.12.1"
-camino = "1.0.2"
+camino = { version = "1.0.2", features = ["serde1"] }
 billboard = { git = "https://github.com/EverlastingBugstopper/billboard.git", branch = "main" }
 chrono = "0.4"
 console = "0.14.0"
 git2 = "0.13.17"
 git-url-parse = "0.3.1"
+harmonizer = "0.1.2"
 heck = "0.3.2"
 humantime = "2.1.0"
 opener = "0.4.1"
@@ -51,10 +52,11 @@ strsim = "0.10"
 serde_json = "1.0"
 structopt = "0.3.21"
 tracing = "0.1.22"
+toml = "0.5"
 regex = "1"
 url = "2.2.0"
 semver = "0.11"
-toml = "0.5"
+serde_yaml = "0.8"
 
 [dev-dependencies]
 assert_cmd = "1.0.1"