Removes installation of CMake during CI

Latest Travis Trusty dist already provides CMake 3.9.2

Fixes Codecov badge

Merges advanced benchmarking branch

Major changes
    + Introduces benchmarking with chrono
    + Sets constant time benchmarks execution

Adds CMake build configuration

Major updates
    + Adds CMake configuration file
    + Adds three CMake targets: gost15 library, selftests and benchmark
    + gost15 library can be built in one of three versions: compact, optimised and SIMD

Minor updates
    + Adds support for GCC and Clang compilers
    + Forces strict language C99 dialect via C_EXTENSIONS and COMPILE_FEATURES

Updates README with information on SIMD implementation

Minor updates
    + Adds details on SIMD implementation version in general

Updates README with information on SIMD implementation

Minor updates
    + Adds details on SIMD implementation version in general