legion 0.4.0

High performance entity component system (ECS) library
Documentation
<!--- Provide a general summary of your changes in the Title above -->

## Description

<!--- Describe your changes in detail -->

<!--- Separate Additions, Removals and Modifications -->




## Motivation and Context

<!--- Why is this change required? What problem does it solve? -->

<!--- If it fixes an open issue, please link to the issue here. -->




## How Has This Been Tested?

<!--- Please describe in detail how you tested your changes. -->




## Checklist:

<!--- Go over all the following points, and put an `x` in all the boxes that apply. -->

<!--- If you're unsure about any of these, don't hesitate to ask. We're here to help! -->

- [ ] Acknowledged that by making this pull request I release this code under an MIT/Apache 2.0 dual licensing scheme.
- [ ] My code follows the code style of this project.
- [ ] If my change required a change to the documentation I have updated the documentation accordingly.
- [ ] I have updated the content of the book if this PR would make the book outdated.
- [ ] I have added tests to cover my changes.
- [ ] My code is used in an example.