* Rename 'BuildRule to 'BuildEdige' because it is the official term
* NinjaParser to handle 'include' and 'rule' directives
* NinjaParser to handle parse "rule name" in 'build' correctly
* Make variable table a simple `[String: String]` and keep any bindings
to make the substitutions possible.
* Generate command line argumets using 'command' variable in the 'rule'
and use it as the source of truth, istead of using random known
bindings like 'FLAGS'.
Generate a new 'SwiftRuntimes' xcodeproj if a build directory
for 'Runtimes' is specified with `--runtimes-build-dir`, along with a
combined 'Swift+Runtimes' workspace.
This is a tool specifically designed to generate
Xcode projects for the Swift repo (as well as a
couple of adjacent repos such as LLVM and Clang).
It aims to provide a much more user-friendly experience
than the CMake Xcode generation (`build-script --xcode`).
