feat: use cargo hakari to reduce crate rebuilds

Large workspaces end up with a very large number of possible build
configurations.

Even worse, the feature set of a package affects everything that depends
on it, so syn being built with a slightly different feature set than
before would cause *every package that directly or transitively depends
on syn to be rebuilt. For large workspaces, this can result a lot of
wasted build time.

To avoid this problem, many large workspaces contain a workspace-hack
crate. The purpose of this package is to ensure that dependencies like
syn are always built with the same feature set no matter which workspace
packages are currently being built. This is done by:

1) adding dependencies like syn to workspace-hack with the full feature
set required by any package in the workspace
2) adding workspace-hack as a dependency of every crate in the
repository.

cargo-hakari manages a workspace-hack crate for you.

examples/single-page/Cargo.toml

@@ -8,4 +8,5 @@ edition = "2018"
 crate-type = [ "dylib" ]
 
 [dependencies]
+cargo-workspace-hack = { version = "0.1", path = "../../../../../infra/cargo-workspace-hack" }