Document use of special parameterized object for captureError

[watson]

The captureError function can take 3 types of arguments in the first position:

• An error object
• A string
• A special type of parameterized object

The latter is currently undocumented.

If captureError is passed an object instead of an error or a string we expect it to be in the format of { message: '...', params: [] }.

Example usage:

agent.captureError({
  message: 'Could not find user %s with id %d in the database',
  params: ['Peter', 42]
})

This makes it possible for us to better group error messages that contain variable data like ID's or names.