Handle workspace modifications

[charlespwd]

Fix #588

Issue summary:

• We didn't know when files were deleted, which caused the textDocument/didClose handler to throw an Errno::ENOENT when trying to "sync" the storage with the file system.

Fix summary:

• Rescue Errno::ENOENT in textDocument/didClose for language clients that do not support the workspace.fileOperations.didDeleteFiles client capability
• Start handling 2 new LSP client->server notifications:
  • workspace/didCreateFiles
  • When we get those, we sync the InMemoryStorage with file contents from the file system
  • workspace/didDeleteFiles
  • When we get those, we remove the files from the InMemoryStorage
• Start handling a new LSP client->server request:
  • workspace/willRenameFiles
  • When we get those, we move the contents of the old path to the new path in the InMemoryStorage, and then remove the content at the old path.