2.6.8 - CRITICAL BUGFIX

2.6.7 broke compile for microchip boards and 1-series parts. This should correct these problems (introduced by the PWM menu in 2.6.7; Note that prior to this,at some point in 2.6.x I had started but not completed work on that feature, and I suspect pwm problems were present in 2.6.6 and earlier that had not been reported on higher pincount parts

This version also fixes behavior of tinyNeoPixel at some (high) clock speeds, and adds an updateLatch() method to let you change the latch timeout (which prevents fast calls to show() from breaking), since the library defaults to the 50 that the datasheet specifies, but it's unclear whether any leds with a 50us timeout actually exist or ever existed: the original ones actually only had a 6us latch timeout, while followon parts have in some cases been willing to wait a whopping 200 us, maybe even 250us, between bits without latching.
megaTinyCore.h library gets a number of fixes and corrections, and more of these examples are now tested so that we don't have examples calling functions that don't exist or calling them by the wrong names.

The analog documentation for getAnalogReference and the table of reference ID's was corrected to reflect megaTinyCore instead of DxCore.
getAnalogReference was also, in fact, missing from wiring_analog.c. This is corrected.