crashreporter: Use a monospace font to view files
crashreporter: Prevent selecting two files
README: Move USE_NATIVE_FS to OPTIONS.md

Normal users don't need to set this.
Dialog: Don't try the next backend on SIGINT

No need to bombard the user with further dialogs if they are trying to
exit already.
Dialog: Set geometry for gxmessage

Otherwise the window ended up very small.
Add convenience wrappers for platform::run*
Use platform::run* wrappers
Prefer OS-specific calls over probing procfs
Improve detection of redirected stdout/stderr
Don't enabled colors if $TERM is unset or "dumb"

This matches the algorithm used by git to determine if we have a color
capable terminal.
Remove DEBUGNPCMOVE global variable

Was always 0.
Remove BUILD_EDITOR configuration variable

Didn't really do anything anymore.
Environment.h: Use \brief for multi-line docs
CrashReporter.h: Use \brief for multi-line docs
OS.h: Use \brief for multi-line docs
Platform.h: Use \brief for multi-line docs
Process.h: Use \brief for multi-line docs
Thread.h: Use \brief for multi-line docs
Time.h: Use \brief for multi-line docs
Move time functions into the platform namespace