Make it possible to pass Unsafe strings as column labels

Handle `Unsafe` strings in column labels. Fixes #89
Add documentation for #89
Merge pull request #90 from glittershark/89/html-as-label

Make it possible to pass Unsafe strings as column labels
Add keywords to package.json
Package.json metadata for npm publish

Add package metadata necessary to publish reactable on npm. This also
bumps the version number to 0.9.3.
Add test.html to npmignore
Fix duplicate code at head of test files
Use JSX spread operator to avoid non-JSX

Use the jsx spread (`{...props}`) operator to avoid the cases where
we're using non-jsx component initialization.
Support null data values
Add class for sortable columns
Merge pull request #96 from glittershark/fix-duplicate-code

Fix duplicate code at head of test files
Merge pull request #97 from glittershark/jsx-cleanup

Use JSX spread operator to avoid non-JSX
Merge pull request #94 from wemcdonald/sortable-header-class

Conflicts:
	build/reactable.js
	src/reactable.jsx
Merge remote-tracking branch 'wemcdonald/handle-null-values'

This is a merge of what used to be #93, before some strange things
happened.

Thanks, @wemcdonald
Expose the filterBy function as a public API

Expose the filterBy() function. Fixes #75
(#75) Add documentation for public filterBy API