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/util/command-interest-generator.hpp b/src/util/command-interest-generator.hpp
index 8b4d796..18bc960 100644
--- a/src/util/command-interest-generator.hpp
+++ b/src/util/command-interest-generator.hpp
@@ -25,7 +25,7 @@
   static const Name DEFAULT_CERTIFICATE_NAME;
 
   CommandInterestGenerator()
-    : m_lastTimestamp(time::now() / 1000000)
+    : m_lastTimestamp(time::toUnixTimestamp(time::system_clock::now()))
   {
   }
 
@@ -36,30 +36,29 @@
 
   void
   generate(Interest& interest, const Name& certificateName = Name());
-  
+
   void
   generateWithIdentity(Interest& interest, const Name& identity);
-  
+
 private:
-  int64_t m_lastTimestamp;
+  time::milliseconds m_lastTimestamp;
   KeyChain m_keyChain;
 };
 
 
 inline void
-CommandInterestGenerator::generate(Interest& interest, 
+CommandInterestGenerator::generate(Interest& interest,
 				   const Name& certificateName /*= Name()*/)
 {
-  int64_t timestamp = time::now() / 1000000;
-  while(timestamp == m_lastTimestamp)
+  time::milliseconds timestamp = time::toUnixTimestamp(time::system_clock::now());
+  while(timestamp <= m_lastTimestamp)
     {
-      usleep(1000); //Guarantee unqiueness of timestamp
-      timestamp = time::now();
+      timestamp += time::milliseconds(1);
     }
 
   Name commandInterestName = interest.getName();
   commandInterestName
-    .append(name::Component::fromNumber(timestamp))
+    .append(name::Component::fromNumber(timestamp.count()))
     .append(name::Component::fromNumber(random::generateWord64()));
   interest.setName(commandInterestName);
 
@@ -70,17 +69,19 @@
 
   m_lastTimestamp = timestamp;
 }
-  
+
 inline void
 CommandInterestGenerator::generateWithIdentity(Interest& interest, const Name& identity)
 {
-  int64_t timestamp = time::now() / 1000000;
-  if(timestamp <= m_lastTimestamp)
-    timestamp = m_lastTimestamp + 1;
+  time::milliseconds timestamp = time::toUnixTimestamp(time::system_clock::now());
+  while(timestamp <= m_lastTimestamp)
+    {
+      timestamp += time::milliseconds(1);
+    }
 
   Name commandInterestName = interest.getName();
   commandInterestName
-    .append(name::Component::fromNumber(timestamp))
+    .append(name::Component::fromNumber(timestamp.count()))
     .append(name::Component::fromNumber(random::generateWord64()));
   interest.setName(commandInterestName);