Changes since s2.02:

 - I forgot to include help.ino in past releases, now it's included.

 - Modified the included library files Keypad.* to make keypad scans impulse noise-resistant. Now key scan has to return
   bit-identical map N_KEY_READS (=3) times in a row to have the change accepted. This fixed the occasional
   fake key triggering during long (>20 minutes) focus stacks.

 - Upgraded all float types to real64 (from real32). Also introduced LONG_TIME macro option in stacker.h; when
   defined, all time related variables get 64-bit integer type. Introduced my own 64-bit version of micros(), in micros_my().
   All these changes are critical to get full stability for long (>20 minutes) continuous stacking shootings.

 - Replaced roundMy() with two functions - round_coords() and round_time(), as they deal with different types.

 - Modified TIMING macro option behaviour. Now it measures the average Arduino loop length, and its std, for the
   most recent move. It is displayed at the left bottom corner when pressing the "*" key. The units are
   microseconds.