HardwareSerial now polls ROM_UARTBusy() in flush/flushAll so .flush() can guarantee UART contents transmitted before user enters suspend/sleep/sleepSeconds.
Base config setting for DeepSleep mode (osc, power modes)
First working edition of sleep/sleepSeconds/suspend - uses SysTick in DeepSleep mode with system clock set to PIOSC/16, or 1MHz.
Fixed up some things, enabled LDO voltage adjustment for TM4C123.  Still need to work & test TM4C129 support.
Using 100ms coarseness for sleep() now, as maximum MOSC startup time can be as high as 18ms according to datasheet.
Merge pull request #519 from energia/issue_519

Prep-work for Tiva/ARM Low Power Sleep modes