Introduce Hoogle server command line option

[SkyWriter]

This PR introduces support for stack hoogle --server option to start local Hoogle server as per #2310.

Here's what I did:

• Added the corresponding option and its handling
• Introduced a record in the ChangeLog.md file for the changes
• I haven't found much info on Hoogle in the docs, so I figured no changes are necessary

The testing was manual by issuing stack hoogle --server on the command line and making sure it works as expected.

As a side note: besides options mentioned in the issue I added -p 8080 to start Hoogle on a non-privileged port. This is the default Hoogle behaviour since 5.0.13 (released on 2017-07-30), but I figured that there may be older versions in the wild. As there's no way to pass options directly to Hoogle via stack hoogle those older versions would try binding to 127.0.0.1:80 and fail without a real way to fix it apart from using stack exec to supply the -p option.

[snoyberg]

Works great, thanks!