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/src/encoding/cryptopp/asn_ext.cpp b/src/encoding/cryptopp/asn_ext.cpp
index beea45d..7741314 100644
--- a/src/encoding/cryptopp/asn_ext.cpp
+++ b/src/encoding/cryptopp/asn_ext.cpp
@@ -17,29 +17,14 @@
 namespace ndn {
 
 size_t
-DEREncodeGeneralTime(CryptoPP::BufferedTransformation &bt, MillisecondsSince1970 time)
+DEREncodeGeneralTime(CryptoPP::BufferedTransformation &bt, const time::system_clock::TimePoint& time)
 {
-  if (time < 0)
-    throw Asn::Error("Calendar time value out of range");
-  else if (time > 2e14)
-    // 2e14 is about the year 8300.  We don't want to go over a 4-digit year.
-    throw Asn::Error("Calendar time value out of range");
+  std::string str = time::toIsoString(time);
+  // For example, 20131226T232254
+  // 20131226T232254.100000
+  BOOST_ASSERT(str.size() >= 15);
+  std::string asn1time = str.substr(0, 8) + str.substr(9,6) + "Z";
 
-
-  boost::posix_time::ptime boostTime =
-    UNIX_EPOCH_TIME + boost::posix_time::milliseconds(time);
-  
-  const boost::format f = boost::format("%04d%02d%02d%02d%02d%02dZ")
-                % boostTime.date().year_month_day().year
-                % boostTime.date().year_month_day().month.as_number()
-                % boostTime.date().year_month_day().day.as_number()
-                % boostTime.time_of_day().hours()
-                % boostTime.time_of_day().minutes()
-                % boostTime.time_of_day().seconds()
-    ;
-
-  std::string asn1time = f.str();
-  
   bt.Put(GENERALIZED_TIME);
   size_t lengthBytes = DERLengthEncode(bt, asn1time.size());
   bt.Put(reinterpret_cast<const uint8_t*>(asn1time.c_str()), asn1time.size());
@@ -47,7 +32,7 @@
 }
 
 void
-BERDecodeTime(CryptoPP::BufferedTransformation &bt, MillisecondsSince1970 &time)
+BERDecodeTime(CryptoPP::BufferedTransformation &bt, time::system_clock::TimePoint& time)
 {
   byte b;
   if (!bt.Get(b) || (b != GENERALIZED_TIME && b != UTC_TIME))
@@ -71,7 +56,7 @@
       str = "19" + str;
   }
  
-  time = fromIsoString(str.substr(0, 8) + "T" + str.substr(8, 6));
+  time = time::fromIsoString(str.substr(0, 8) + "T" + str.substr(8, 6));
 }
 
 } // namespace ndn