Property descriptor field "writable". Fixes gh-269

Signed-off-by: Rick Waldron <waldron.rick@gmail.com>
Fix for #263
process.platform and require('os').platform() is now the same
process.arch and require('os').arch() is now the same too

Also arch is now 'arm' instead of 'thumb2'
Fix for #263. Arch set to armv7-m
Merge pull request #272 from rwaldron/269

Property descriptor field "writable". Fixes gh-269
Merge pull request #280 from Olegas/fix-process-platform

Make require('os').platform()/arch() returns the same as process.platform/arch
failing test for https://github.com/tessel/runtime/issues/275
implement util.format with a bunch of tests [several failing due to colony issues]