This PR implements #1667 with some modifications.

The presence of a tsconfig.json file in a directory indicates that the directory is the root of a TypeScript project. The tsconfig.json file specifies the root files and the compiler options required to compile the project. A project is compiled in one of the following ways:

• By invoking tsc with no input files, in which case the compiler searches for the tsconfig.json file starting in the current directory and continuing up the parent directory chain.
• By invoking tsc with no input files and a -project (or just -p) command line option that specifies the path of a directory containing a tsconfig.json file.

When input files are specified on the command line, tsconfig.json files are ignored.

An example tsconfig.json file:

{
    "compilerOptions": {
        "module": "commonjs",
        "noImplicitAny": true,
        "removeComments": true,
        "preserveConstEnums": true,
        "out": "../../built/local/tsc.js",
        "sourceMap": true,
    },
    "files": [
        "core.ts",
        "sys.ts",
        "types.ts",
        "scanner.ts",
        "parser.ts",
        "utilities.ts",
        "binder.ts",
        "checker.ts",
        "emitter.ts",
        "program.ts",
        "commandLineParser.ts",
        "tsc.ts",
        "diagnosticInformationMap.generated.ts"
    ]
}

The "compilerOptions" property can be omitted, in which case the compiler's defaults are used.

If no "files" property is present in a tsconfig.json, the compiler defaults to including all files the containing directory and subdirectories. When a "files" property is specified, only those files are included.

A tsconfig.json file is permitted to be completely empty, which compiles all files in the containing directory and subdirectories with the default compiler options.

Compiler options specified on the command line override those specified in the tsconfig.json file.