v0.35

• new category "Sitherm Pro"; caution: category numbers all move up by one, starting from category "Wärmepumpe" (from 20 to 21) onwards.
• graph display of logging data now comes with crosshair and shows detailed values as tooltip
• improved SD-card output by factor 3 (from 16 to 45 kbps), switching SD-card library from from SD.h to SdFat.h (https://github.com/greiman/SdFat) brings another 10% performance boost
• adjusted paths and directory layout of SdFat to enable compiling from sketch directory.
• new data type vt_sint for signed int data, currently only used in some Sitherm Pro parameters