Patch which enables sleepAbort() macro to be used inside ISRs for cancelling LPM3/4 sleep mode.
Reworked sleeping variables so stay_asleep is used by ISRs, not sleeping; also added LPM4 as suspend()
Cleaned up the comments in the various sleep/suspend functions.
Added stay_asleep hooks to USCI ISRs to support I2C slave mode; I2C slave user ISR may issue wakeup() to abort LPM3/4.  Also fixed an uncaught bug in USCI_B1 ISR where an extra } was present.
Oops; misspelled my still_asleep flag variable in many instances.
Added API-level lm4f/tm4c support for sleep, sleepSeconds, wakeup.  Just uses delayMicroseconds under the hood for now.
I realized delay & sleep implementations used an overloaded local "milliseconds" variable; changed to "ms" to avoid confusion.
Merge pull request #384 from energia/issue_384

Low Power Sleep - Ability to interrupt sleep mode inside ISRs