Implement Serial.availableForWrite() for serial emulation

Improve String support for 64 bit integers

Similar startup delay code between Teensy 3 and 4

Merge pull request #623 from ssilverman/issue-591

Fix Print::printf() to call va_end()

Adding 1.55 release tag

Add empty CrashReport on Teensy 2.0, LC, 3.x

Fix AudioProcessorUsage() on Teensy LC

Workaround for USB memory bandwidth at very slow CPU speeds

Merge pull request #433 from FrankBoesing/patch-3

shiftout: highest speed 10MHz

Merge pull request #427 from FrankBoesing/patch-1

SCB_ID_CSSELR is not const