This commits adds support for "--config" flag in "deno install"
subcommand. Specified configuration file is copied alongside
source code to installation directory.
$HOME is meaningless on Windows. It may be set by users or by third
party software, but it is non-standard and should not be relied upon.
Likewise, $USERPROFILE is meaningless on other platforms.
* rewrite test runner in Rust
* migrate "test" and "runTests" functions from std to "Deno" namespace
* use "Deno.test()" to run internal JS unit tests
* remove std downloads for Deno subcommands
* Use PathBuf for DenoSubcommand::Bundle's out_file
* Use PathBuf for DenoSubcommand::Format's files
* Use PathBuf for DenoSubcommand::Install's dir
* Use PathBuf for read/write whitelists
