* globally expose repeat functionality as advanced function
* implement repeated sends for Arduino based boards
* use String class instead of C-style arrays to benefit from dynamic allocation and avoid buffer overflows. Try to improve stability of BME280.
* replace sprintf with String class to avoid buffer overruns by dynamic allocation
* fix caps on variable
* re-add TSL2561 code that was accidentally removed
* Add support for TSL2561 based light intensity measurement
* replace Serial prints with trc, add TSL2561 code to test config
* add Adafruit TSL2561 lib to Travis config
* avoid multiple definitions and fix missing string constructor in trace