v2.0.0

Next generation of uptime_cpp

Now more fetching of uptime value on every call, instead makes a timepoint on it on constructor.
Downside is that there is more to calculate, but for that; there is data() member function to calculate
all fields at once.

Also, it's now more portable. Unfortunately I have no possibility to test it on other architectures except
Linux and OS X; but it should work on others as well.