Remove build condition to prevent old strings hanging around
Add -h option to build.bat

- update installer ReadMe file
- suppress installer per-file byte-compilation messages to system log
- speed up installer byte-compilation
- isolate ensurepip install from user site-packages

Fixes warnings when building python3.dll due to the .def file accumulating multiple copies of each line.
Adds shebang line to prepare_ssl so it will run with py.exe.

collections.abc.Awaitable and collections.abc.Coroutine no longer
use __instancecheck__ hook to detect generator-based coroutines.

inspect.isawaitable() can be used to detect generator-based coroutines
and to distinguish them from regular generator objects.

Patch by Petr Viktorin.

Patch by Benno Leslie and Yury Selivanov.

positives with the -flto option (gcc >= 4.9.0 and clang).

Patch by Martin Panter.

Suggested by Martin Panter.

isawaitable() was added before collections.abc.Awaitable; now,
with Awaitable, it is no longer needed (we don't have ishashable()
or isiterable() methods in the inspect module either).

A deprecation warning no longer issued by XMLParser subclass with default
doctype() method.  Direct call of doctype() now issues a warning.  Parser's
doctype() now is not called if target's doctype() is called.  Based on patch
by Martin Panter.

A deprecation warning no longer issued by XMLParser subclass with default
doctype() method.  Direct call of doctype() now issues a warning.  Parser's
doctype() now is not called if target's doctype() is called.  Based on patch
by Martin Panter.

object now always allocates place for trailing null byte and it's buffer now
is always null-terminated.