Type declarations for missing properties

[janpaepke]

This PR adds type definitions for the static values for INITIALIZING, CONNECTING, OPEN and CLOSED.
This is a backwards compatible change.

I also took the liberty of optimizing the build, since the d.ts file should be generated from the jsdoc.
Unfortunately it seems the sse.d.ts file was updated manually in 5471ff1, so it is out of sync with the source. This also means the sourcemap is inaccurate.

I fixed this as best I can, but with one caveat: The constructor (new (url: string, options?: SSEOptions): SSE;) cannot be extracted from jsdoc using tsc.
This is due to the fact that SSE is defined as a type, when it should be instance or class.
Consequently, when running tsc the constructor will be removed from the d.ts and needs to be added back in manually.
I don't think there is a workaround for this (or at least I didn't find any).

To get the output back in sync with the source, a more extensive rewrite of the types is likely due and should probably be tested using tsd or the like.

When considering such a rewrite however, my recommendation would be to refactor the code to use typescript with ecma 6 classes.
This way you could ensure compatibility with EventSource (extends EventSource) and get proper always-in-sync type definitions for free without the effort of separate definitions.

[janpaepke]

thanks for merging.

would you consider releasing a patch version including this? :)

[mpetazzoni]

Done!

[janpaepke]

you might also want to publish the new version to npm. ;)

[mpetazzoni]

🤦🏻 Done!