all: Refactoring work with time using boost::chrono

Now the library has two clocks: time::steady_clock and
time::system_clock, following (boost|std)::chrono.  In addition to
standard now() method, the library contains several helpers to convert
to/from UnixTimestamp (microsecond resolution) and IsoString (optional
microsecond resolution).  The IsoString conversions use
boost::posix_time routines, since boost::chrono supports extended IO
support only starting boost version 1.52 (Boost Chrono V2).

This commit breaks compatibility with previous API.  All time-related
Data/Interest calls must explicitly use time units to specify
FreshnessPeriod/InterestLifetime.

Brief usage/conversion guide:

- creation of time units does not support double/float types.  If
  necessary to create time unit from double, ``ndn::duration<double>`` (for
  seconds) needs to be used instead.  In some cases, this would also
  require ``ndn::duration_cast``, if the target is not ``ndn::nanoseconds``.
- ndn::getNow, ndn::ndn_getNowMilliseconds, ndn::time::now are all
  removed in favor of the now() method in a specific clock:

    * time::system_clock::now();
    * time::steady_clock::now();

- When necessary to convert system_clock::TimePoint to unix timestamp,
  ``time::toUnixTimestamp`` can be used.  This method return number of
  milliseconds since UNIX epoch as ``ndn::time::milliseconds`` type.
  Use count() method to obtain number as an integral value.

Change-Id: Icd688bc6766e008d60c3d2888173627874526e47
Refs: #1152
diff --git a/tests/management/test-nrd.cpp b/tests/management/test-nrd.cpp
index de95ee2..92622f0 100644
--- a/tests/management/test-nrd.cpp
+++ b/tests/management/test-nrd.cpp
@@ -39,7 +39,7 @@
   std::ostringstream os;
   os << opt;
   BOOST_CHECK_EQUAL(os.str(), "PrefixRegOptions(Prefix: /localhost/reg/test, "
-                    "FaceID: 0, Flags: 1, Cost: 0, ExpirationPeriod: -1, Protocol: )");
+                    "FaceID: 0, Flags: 1, Cost: 0, ExpirationPeriod: -9223372036854775808 milliseconds, Protocol: )");
 }
 
 BOOST_AUTO_TEST_CASE (PrefixRegOptionsDecoding)