Actions:
* Remove superfluous includes to boost/date_time, iostream, and pragma_comp_defs.h
* Include cstdio for snprintf
* Include string for std::string
* Move get_gmt_time to top of module for following step
* Use thread-safe get_gmt_time instead of unsafe gm_time in function get_internet_time_str()
* In get_time_interval_string(), add explicit (int) casts to git rid of VS4996 warnings
* In get_time_interval_string(), use snprintf instead of boost::lexical_casts and string concats
* In file epee_utils.cpp, include boost/range/iterator_range.hpp for boost::make_iterator_range.
Previously, epee_util.cpp was including some file which was including time_helper which included
a boost header which included iterator_range.hpp at some point, which allowed epee_util.cpp to
compile without an explicit include of iterator_range.hpp. I added it because I removed the boost
includes in the first step which broke epee_util.cpp.
Actions:
* Move get_ns_count(), get_tick_count(), and get_gmt_time() from misc_os_dependent.h to time_helper.h. I did this because all those functions are time-related and under the same namespace
* Remove misc_os_dependent.h because it is now empty
* Change all includes of misc_os_dependent.h to time_helper.h where appropriate
* Remove get_time_string*() from time_helper.h b/c its unused
* Remove get_time_t_from_ole_date() from time_helper.h b/c its unused
* Remove odbc_time_to_oledb_taime() from time_helper.h b/c its unused
* Refactor get_ns_count() to use std::chrono instead of 4 different implementation-specific hacks
