* core additions:
   * added erase_if, similar in function to <algorithm>s remove_if, but calling erase on an stl container instead
   * added unix_timestamp() and unix_timestamp(chrono::time_point) which returns the unix timestamp in seconds of the current time or the given time_point resp.
   * added interpolate(), simple linear interpolation
   * extended get_file_list(...) so that the extension filter can optionally not be applied to folder names (-> always get folders); also added automatic decomposed -> precomposed name conversion on osx
 * all mouse events now also store a pressure value (this is due to SDL treating graphic tablet events as mouse events); note that this needs an SDL patch to actually work (+it'll only work on osx right now)
 * fixed finger pressure and finger motion events (everything is stored+handled as normalized floats now)
 * reworked file_ios reading and writing of sized unsigned ints: all functions now take or return sized uint types (supported are uint8_t, uint16_t, uint32_t and uint64_t)
 * added move constructor and assignment to file_io
 * extended file_io::FILE_TYPE to include misc generic types and a2elight types
 * added floor_packed macro (extends to __attribute__((packed)) with clang/gcc)
 * added utf8_decomp_to_precomp to unicode class (this is only enabled/needed on osx and ios)
 * added some logic/bit/relational ops to vector2 class
 * fixed reading the screen.dpi value from the config
 * added get_computer_name() function to osx_helper and ios_helper (returns the localized and human-readable computer name)
 * thread_base: on osx, this now calls pthread_setname_np(...) to set the thread name so that it can be seen in the debugger (this should work on other platforms that use pthread based std::threads as well, but I'm not sure how to check for this right now); also added get_thread_name() function
 * removed hash<EVENT_TYPE> workaround now that this works as-is in c++14
 * xcode project: added include folders (-isystem) for /usr/include and libc++ in the xcode toolchain (-> inside the Xcode.app)
 * updated README (min SDL version required is now 2.0.2 -> manual GLES3 patch is no longer necessary)