fix: error emitted from one hover provider would break other hover pr…

…oviders (#117)

feat: supply sourcegraphURL and clientApplication to extensions

In some cases, such as to work around https://github.com/sourcegraph/sourcegraph/issues/566, it is useful for extensions to know the Sourcegraph URL and what kind of client application is running it.

feat: support themeable decorations (light vs. dark styles)

Decorations may now specify different styles for light vs. dark themes. The light/dark styles override the base styles when there is overlap.

feat: createPanelView API for extension panels with custom Markdown

Extensions can use the new `sourcegraph.app.createPanelView` API to add panels to the UI. These panels can contain Markdown.

feat: add search query transformer extensibility point (#95)

* adds a new search namespace
* adds query transformer extensibility point

fix: propagate stack traces

fix: suppress connection error when disabling an extension (#91)

refactor: remove unneeded Component, use visibleTextDocuments directly

This suffices for a while.

BREAKING CHANGE: The environment component has been removed; now you need to specify the visible text documents directly.

feat: remove sourcegraphURL from extension API

It was not used and is not necessary.

feat: sourcegraphURL for extensions, passing through init data