Add changelog and bump version for proposed 4.1.0 initial bi-weekly release #298

[alamb]

re #292.

Supercedes #298 (the initial version)

NOTE: This PR targets the active_release branch, NOT master

Rationale:

Begin preparing for the first bi weekly release

Changes:

1. Add changelog (see rendered version)
2. I made some manual edits to the changelog while reviewing them. I left the touchups in a separate commit
3. Update version to 4.1.0

Notes

I chose to call this 4.1.0 as there are some "featurettes" and new APIs such as #25 and #210.

Notes:

• Process is documented in Document and automate new release process #299 (still a WIP)

Verson was updated using (on a Mac):

sed -i '' -e 's/5.0.0-SNAPSHOT/4.1.0/g' `find . -name 'Cargo.toml'`

[andygrove]

LGTM

[jorgecarleitao]

Looks great!