Operator Scan Backpressure Fix

Problem 1) The initial value was being emitted before subscription which caused issues with request/producer state, particularly if filter() was used to skip that initial value and then called request(1) before the real request had been sent.
Problem 2) The initial value was not accounted for by the request so it was sending 1 more value than requested. It now modifies the request to account for it.
Problem 3) Redo relied upon these nuances to work. I've fixed this by using a simpler implementation that just maintains state within a map function.
Merge pull request #1652 from benjchristensen/1.x-scan-backpressure-fix

Operator Scan Backpressure Fix
0.20.3
Update CHANGES.md
1.0.0-rc.2
1.0.0-rc.2
Removing deprecated operators from operator decision trees
Fix Javadoc README link
Merge pull request #1665 from loganlinn/patch-1

Fix Javadoc README link
Update README.md
Update CONTRIBUTING.md

Added 0.x and 1.x branches.
Fix the bug that Switch doesn't propagate 'unsubscribe'
OperatorScan should check for MAX_VALUE on request
Ignore furthur messages after entering terminate state
Error Handling Unsubscribe and Terminal State
Make TakeUntil obey Rx contract
0.20.4 and 1.0.0-rc.3
Merge pull request #1672 from benjchristensen/merge-0_20_4

Merge 0.20.4 Fixes
fix typo
Remove CloudBees and Pull Request Logo

- migrating to Travis
- Makes no sense to show the pull request build status as there can be many and any of them could fail without meaning anything for the project.