* Introduce facts-tracker
We want to be able to track various things like number of files that are flowified, number of tests passing with Fiber...
This introduces a tool that lets you do that. The API is very simple, you execute the script with a list of tuples [key value] and it's going to create a `facts` branch and put a txt file for each fact and values over time.
```
node scripts/facts-tracker/index.js \
"flow-files" "$COUNT_WITH_FLOW/$COUNT_ALL_FILES"
```
Test Plan:
This is tricky to test because Travis only exposes the private variables (github token) when it processes a committed file and not on branches. The reason is that otherwise anyone could send a pull requests that does `echo $GITHUB_TOKEN` and steal your token.
Given this constraint, I did all the work using two of my repos:
- https://github.com/vjeux/facts-tracker
- https://github.com/vjeux/facts-tracker-test
and am sending this pull request that should work as is /fingers crossed/, but we won't be able to test it out until it is committed.
Note that once this lands, I'm going to kill those two repos.
* Update with all the suggested changes
* Branch on a flow type in travis.yml
* Use $GITHUB_TOKEN
* properly escape it
