Vendor dependencies

Let's see how I like this workflow.

vendor/proc-macro2/Cargo.toml

@@ -0,0 +1,63 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies.
+#
+# If you are reading this file be aware that the original Cargo.toml
+# will likely look very different (and much more reasonable).
+# See Cargo.toml.orig for the original contents.
+
+[package]
+edition = "2018"
+rust-version = "1.31"
+name = "proc-macro2"
+version = "1.0.49"
+authors = [
+    "David Tolnay <dtolnay@gmail.com>",
+    "Alex Crichton <alex@alexcrichton.com>",
+]
+autobenches = false
+description = "A substitute implementation of the compiler's `proc_macro` API to decouple token-based libraries from the procedural macro use case."
+documentation = "https://docs.rs/proc-macro2"
+readme = "README.md"
+keywords = [
+    "macros",
+    "syn",
+]
+categories = ["development-tools::procedural-macro-helpers"]
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/dtolnay/proc-macro2"
+
+[package.metadata.docs.rs]
+rustc-args = [
+    "--cfg",
+    "procmacro2_semver_exempt",
+]
+rustdoc-args = [
+    "--cfg",
+    "procmacro2_semver_exempt",
+    "--cfg",
+    "doc_cfg",
+]
+targets = ["x86_64-unknown-linux-gnu"]
+
+[package.metadata.playground]
+features = ["span-locations"]
+
+[lib]
+doc-scrape-examples = false
+
+[dependencies.unicode-ident]
+version = "1.0"
+
+[dev-dependencies.quote]
+version = "1.0"
+default_features = false
+
+[features]
+default = ["proc-macro"]
+nightly = []
+proc-macro = []
+span-locations = []