Grow TxQ expected size quickly, shrink slowly (RIPD-1534):

* Stores recent history of "good" ledgers. Uses the maximum as the
  expected ledger size. When a large value drops off, use a 90%
  backoff to go down to to the new maximum.
* If consensus is unhealthy, wipe the history in addition to the current
  clamping.
* Include .md doc files in xcode and VS projects

src/ripple/app/misc/impl/TxQ.cpp

@@ -29,6 +29,7 @@
 #include <boost/algorithm/clamp.hpp>
 #include <limits>
 #include <numeric>
+#include <algorithm>
 
 namespace ripple {
 
@@ -107,16 +108,32 @@ TxQ::FeeMetrics::update(Application& app,
         // so clamp down on limits.
         txnsExpected_ = boost::algorithm::clamp(feeLevels.size(),
             minimumTxnCount_, targetTxnCount_);
+        recentTxnCounts_.clear();
     }
     else if (feeLevels.size() > txnsExpected_ ||
         feeLevels.size() > targetTxnCount_)
     {
+        recentTxnCounts_.push_back(feeLevels.size());
+        auto const iter = std::max_element(recentTxnCounts_.begin(),
+            recentTxnCounts_.end());
+        BOOST_ASSERT(iter != recentTxnCounts_.end());
+        auto const next = [&]
+        {
+            // Grow quickly: If the max_element is >= the
+            // current size limit, use it.
+            if (*iter >= txnsExpected_)
+                return *iter;
+            // Shrink slowly: If the max_element is < the
+            // current size limit, use a limit that is
+            // 90% of the way from max_element to the
+            // current size limit.
+            return (txnsExpected_ * 9 + *iter) / 10;
+        }();
         // Ledgers are processing in a timely manner,
         // so keep the limit high, but don't let it
         // grow without bound.
-        txnsExpected_ = maximumTxnCount_ ?
-            std::min(feeLevels.size(), *maximumTxnCount_) :
-            feeLevels.size();
+        txnsExpected_ = std::min(next,
+            maximumTxnCount_.value_or(next));
     }
 
     if (feeLevels.empty())