[Counters] added a new library for handling Countees

- Counters library allows to handle persistant (EEPROM) integer
counters. Library is supposed to be compiled and linked as a static
library
- Counter class allows to handle a single counter
- Counters class allows to handle a group of counters
[AnalogSensors] Minor fix in documentation
[Logger] added a new library for logging messages

- Logger library allows to log message, whatever the destination is
.Library is supposed to be compiled and linked as a static library
- For the moment, the Logger class allows only to log messages in a file
on a SD card
[Logger] removed SD wiring and initialization related code

- Logger library is no longer responsible for SD card wiring and
initialization (SD chip select pin is supposed to be configured before
using this library, and SD library is also supposed to be properly
initialized by a call to SD.begin
[Logger] replaced singleton instance by a constructor

- Logger now longer declares the singleton instance LOGGER but declares
a constructor taking as parameter a SDClass pointer. It allows to use
multiple logger instances to log on multiple SD cards if needed
Merge branch 'master' of https://github.com/sebastienjean/arduino-yasolibs.git
[Counters] cleaned up code

- minor clean ups have been performed
- Counters class constructor now declares Counter ** as parameter
instead of Counter[] *