fix compile error about noreturn on windows
Merge pull request #527 from wang-bin/compile_fix

fix compile error about noreturn on windows
move test virtual time "now_" into VirtualFileSystem

It's the only piece that cares about the current time.
split FakeCommandRunner out of BuildTest

Separating concerns to make a subsequent refactoring easier.
sync version number in master with release

Update RELEASING with notes on how to not screw this up again.
add DepsLog, a new data structure for dependency information

DepsLog is a compact serialization of dependency information.
It can be used to replace depfiles for faster loading.
pass command results via a struct

WaitForCommand now passes all command output via a struct.
This will allow adding more output in a future change.
factor out implicit dep loading
use DepsLog in loading dependencies

WIP
factor out creation of build directory
load deps log at startup
no error if deps log doesn't exist
plumb DepsLog load through Builder
expand DepsLog test, fix two bugs it revealed
track deps log load time in metrics
add "special=gcc" attribute, use to load depslog
windows: add uint16 casts in depslog
factor MSVC parsing out of CLWrapper into CLParser
refactor build-time deps-extraction
windows: use CLParser to extract deps during build