* Fix compilation on Android with GNU STL
GNU STL in Android NDK lacks string conversion functions from C++11, including std::stoul, std::stoi, and std::stod.
This patch reimplements these functions in benchmark:: namespace using C-style equivalents from C++03.
* Avoid use of log2 which doesn't exist in Android GNU STL
GNU STL in Android NDK lacks log2 function from C99/C++11.
This patch replaces their use in the code with double log(double) function.
* format all documents according to contributor guidelines and specifications
use clang-format on/off to stop formatting when it makes excessively poor decisions
* format all tests as well, and mark blocks which change too much
* Rename StringXxx to StrXxx in string_util.h and its users
This makes the naming consistent within string_util and moves is the
Abseil convention.
* Style guide is 2 spaces before end of line "//" comments
* Rename StrPrintF/StringPrintF to StrFormat for absl compatibility.
When generating a human-readable number for user counters, we don't
generally expect 1k to be 1024. This is the default due to the more
general purpose string utility.
Fixes#437
