Fetch pybind through cmake

Removes pybind from 3rdParty folder and instead fetches it during build as discussed in #106 (closed)

3rdParty/pybind11/pybind11-2.6.0/.github/ISSUE_TEMPLATE/bug-report.md

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-name: Bug Report
-about: File an issue about a bug
-title: "[BUG] "
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-Make sure you've completed the following steps before submitting your issue -- thank you!
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-1. Make sure you've read the [documentation][]. Your issue may be addressed there.
-2. Search the [issue tracker][] to verify that this hasn't already been reported. +1 or comment there if it has.
-3. Consider asking first in the [Gitter chat room][].
-4. Include a self-contained and minimal piece of code that reproduces the problem. If that's not possible, try to make the description as clear as possible.
-    a. If possible, make a PR with a new, failing test to give us a starting point to work on!
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-[documentation]: https://pybind11.readthedocs.io
-[issue tracker]: https://github.com/pybind/pybind11/issues
-[Gitter chat room]: https://gitter.im/pybind/Lobby
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-*After reading, remove this checklist and the template text in parentheses below.*
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-## Issue description
-
-(Provide a short description, state the expected behavior and what actually happens.)
-
-## Reproducible example code
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-(The code should be minimal, have no external dependencies, isolate the function(s) that cause breakage. Submit matched and complete C++ and Python snippets that can be easily compiled and run to diagnose the issue.)