Jupyterlab-spreadsheet

- Chore: JupyterLab 1.0 compatibility

This release includes no functional changes. Minor version was bumped to prevent
existing installs from fetching an incompatible version before a JupyterLab
upgrade.

0.0.4 was incorrectly released, causing issues for end users on *nix platforms.
This release corrected that.

- Add: Sheet Picker

The sheet picker lives below the sheet, and allows you to switch between sheets
in a workbook.
This was intended for `0.1.0`, but adding row heights will require either a fork
of SlickGrid, or a whole new grid. I don't want to release a UX-breaking change
as a minor release, so this got bumped up.

- Fix: Row Indexing starts at 1 (4)
- Fix: Model indexing left off last row and column
- Add: Cell Merges

The grid now supports cell merges! Merges work horizontally, vertically, or
both.

- Bugfix release: add keywords to NPM registry

This was released shortly after 0.0.1, and added community-standard keywords
to make this plugin discoverable.

- Initial release.