Update NPM scripts and documentation (#1146)

* Group more test npm scripts into `test:`

* Update documentations on the development workflow

* Update .travis.yml to match updated NPM scripts

* Run npm install in Travis

CONTRIBUTING.md

@@ -37,7 +37,7 @@ your symbol in TeX surrounded by other different kinds of symbols, and seeing
 whether your spacing matches the spacing that TeX produces.
 
 Once your symbol works, check the JavaScript console to make sure you don't get
-a message like "Can't find character metrics for _" when you render your symbol.
+a message like "Can't find character metrics for \_" when you render your symbol.
 If you do, check out [extract_ttfs.py](metrics/extract_ttfs.py).
 
 #### Adding new functions
@@ -87,6 +87,12 @@ tests when you submit a pull request, in case you forget.
 
 If you make any changes to Parser.js, add Jest tests to ensure they work.
 
+Some tests verify the structure of the output tree using [snapshot testing](https://facebook.github.io/jest/docs/en/snapshot-testing.html).
+Those snapshots can be updated by running `npm run test:jest:update`.
+
+Also, test code coverage can be collected by `npm run test:jest:coverage`.
+You can view the report in `coverage/lcov-report/index.html`.
+
 #### Screenshot tests
 
 To ensure the final output looks good, we screenshot different expressions.
@@ -117,6 +123,11 @@ is hard to test new changes in many browsers. If you can, please test your
 changes in as many browsers as possible. In particular, if you make CSS changes,
 try to test in IE 9, using [modern.ie](http://modern.ie) VMs.
 
+## Building
+
+KaTeX is built using webpack with configuration `webpack.config.js`. Run
+`npm run build` to build the project.
+
 ## Style guide
 
 Code
@@ -130,6 +141,13 @@ Code
 
 In general, try to make your code blend in with the surrounding code.
 
+The code can be linted by running `npm run test:lint`, which lints JavaScript
+files using ESLint and stylesheets using stylelint. They must pass to commit
+the changes.
+
+Some files have flowtype annotations and can be checked for type errors using
+Flow by running `npm run test:flow`. See [Flow](https://flow.org/) for more details.
+
 ## Pull Requests
 
  - link back to the original issue(s) whenever possible
@@ -137,7 +155,7 @@ In general, try to make your code blend in with the surrounding code.
  - commits should be squashed before merging
  - large pull requests should be broken into separate pull requests (or multiple logically cohesive commits), if possible
 
- ## Working with submodules
+## Working with submodules
 
 The fonts for KaTeX live in a submodule which appears in submodules/katex-fonts.
 Most of the time you won't have to worry about this unless you're making
@@ -160,6 +178,7 @@ about how to use git submodules see https://chrisjean.com/git-submodules-adding-
 
 When submitting pull requests, that update katex-fonts, you'll need to submit
 two pull requests: one for [KaTeX/katex-fonts](https:/github.com/KaTeX/katex-fonts) and one for [Khan/KaTeX](https://github.com/Khan/KaTeX).
+
 ## CLA
 
 In order to contribute to KaTeX, you must first sign the CLA, found at www.khanacademy.org/r/cla