Investigate etimer to improve low power mode

[mtusnio]

Currently timer1 interrupts the device every 1/1024 of a second which increases energy usage.

See if CP0 count register could be used to compute ticks.

[mtusnio]

Section 2.12 of the reference manual - http://ww1.microchip.com/downloads/en/DeviceDoc/PIC32MX_FRM_Sect02_CPU_61113B.pdf - mentions the CP0 registers we can use.