Simple class to manage a task queue that is serviced by one or
more threads.

This class groups transactions that have been confirmed in blocks into buckets, based on either their fee or their priority.  Then for each bucket, the class calculates what percentage of the transactions were confirmed within various numbers of blocks.  It does this by keeping an exponentially decaying moving history for each bucket and confirm block count of the percentage of transactions in that bucket that were confirmed within that number of blocks.

-Eliminate txs which didn't have all inputs available at entry from fee/pri calcs

-Add dynamic breakpoints and tracking of confirmation delays in mempool transactions

-Remove old CMinerPolicyEstimator and CBlockAverage code

-New smartfees.py

-Pass a flag to the estimation code, using IsInitialBlockDownload as a proxy for when we are still catching up and we shouldn't be counting how many blocks it takes for transactions to be included.

-Add a policyestimator unit test

Pagelocker is only needed for secure (usually wallet) operations, so don't make
the zero-after-free allocator depend on it.

could once be renamed from /src/wallet to /src/legacywallet.

- Detect endian instead of stopping configure on big-endian
- Add `byteswap.h` and `endian.h` header for compatibility with
  Windows and other operating systems that don't come with them
- Update `crypto/common.h` functions to use compat
  endian header

This was added a while ago for testing purposes, but was never intended to be
used. Remove it until upstream libsecp256k1 decides that verification is
stable/ready.

Backwards-compatibility for libstdc++ is not limited to straightforward abi
changes. Symbol visibility also needs to be taken into consideration, and
that really can't be addressed simply.

Instead, just static-link libstdc++ for backwards-compat.

This makes it easier for us to replace it if desired, since it's now only in
one spot. Also, it avoids the openssl include from allocators.h, which
essentially forced openssl to be included from every compilation unit.

Introduce new opaque implementation of `uint256`, move old
"arithmetic" implementation to `arith_uint256.

Credit BlueMatt for libbitcoinsonsensus.h/cpp

For windows builds, exe's are always static, but libs should still conform to
--enabled-shared and --enable-static.

Attempt to codify the possible error statuses associated with script
validation. script/types.h has been created with the expectation that it will
be part of the public lib interface. The other flag enums will be moved here in
a future commit.

Logging has also been removed in order to drop the dependency on core.h. It can
be re-added to bitcoind as-needed. This makes script verification finally free
of application state and boost!