contrib/packaging/inno/requirements.txt.in

inno: script to automate building Inno installer

The official Inno installer build process is poorly documented.
And attempting to reproduce behavior of the installer uploaded
to www.mercurial-scm.org has revealed a number of unexpected
behaviors.

This commit attempts to improve the state of reproducibility
of the Inno installer by introducing a Python script to
largely automate the building of the installer.

The new script (which must be run from an environment with the
Visual C++ environment configured) takes care of producing an
Inno installer. When run from a fresh Mercurial source checkout
with all the proper system dependencies (the VC++ toolchain,
Windows 10 SDK, and Inno tools) installed, it "just works."
The script takes care of downloading all the Python
dependencies in a secure manner and manages the build
environment for you. You don't need any additional config
files: just launch the script, pointing it at an existing
Python and ISCC binary and it takes care of the rest.

The produced installer creates a Mercurial installation with
a handful of differences from the existing 4.9 installers
(produced by someone else):

* add_path.exe is missing (this was removed a few changesets ago)
* The set of api-ms-win-core-* DLLs is different (I suspect this
  is due to me using a different UCRT / Windows version).
* kernelbase.dll and msasn1.dll are missing.
* There are a different set of .pyc files for dulwich,
  keyring, and pygments due to us using the latest versions of
  each.
* We include Tcl/Tk DLLs and .pyc files (I'm not sure why these
  are missing from the existing installers).
* We include the urllib3 and win32ctypes packages (which are
  dependencies of dulwich and pywin32, respectively). I'm not
  sure why these aren't present in the existing installers.
* We include a different set of files for the distutils package.
  I'm not sure why. But it should be harmless.
* We include the docutils package (it is getting picked up as
  a dependency somehow). I think this is fine.
* We include a copy of argparse.pyc. I'm not sure why this was
  missing from existing installers.
* We don't have a copy of sqlite3/dump.pyc. I'm not sure why. The
  SQLite C extension code only imports this module when
  conn.iterdump() is called. It should be safe to omit.
* We include files in the email.test and test packages. The set of
  files is small and their presence should be harmless.

The new script and support code is written in Python 3 because
it is brand new and independent code and I don't believe new
Python projects should be using Python 2 in 2019 if they have
a choice about it.

The readme.txt file has been renamed to readme.rst and overhauled
to reflect the existence of build.py.

Differential Revision: https://phab.mercurial-scm.org/D6066

docutils
dulwich
keyring
pygments
pywin32