created Options interface

[jpfluger]

Options interface exposes the private options struct without breaking code, so this is backwards-compatible. Only getters are available on the interface. set functions could be added later, if desired. The interface is available through the manager.Opts() function. Added a single test function that compares against defaults.

• This should satisfy issue Add manager.Opts() method to expose option #30.
• Opts() allows web frameworks (eg echo) to create middleware that will play nicely with scs. See issues The problem of log.Println() in Use() function #24 and problems with using wrapping Use for echo.

There are two additional commits associated with this pull request. This was actually unintended b/c I began the pull request before the 2nd two commits were added but Github automatically added them to this request. I can try splitting out, if you want.

All three commits are backwards-compatible with the defaults.

Re. saved property to session: helps the backend data store determine stale records. Also required by TouchWithInterval() to know if Touch() should occur. In order to preserve strict backwards compatibility, I added a manager.UseSaved() function. If the opts.useSaved value is true, only then will the date be saved in the sessions store.

Re. TouchWithInterval: limits amount of unnecessary writes to back end data store. This would close #32.

I have an an echo middleware example but will wait to commit and have that conversation after we can get past these. Thanks!

[alexedwards]

Could you split the Opts() commit out from the other two? I'm happy to merge that one, but want to think about the other two.

[jpfluger]

I removed the last two commits. Much better. FYI, I used this gist successfully. I had first tried git rebase -i that worked locally but not upstream.

[jpfluger]

I'll create a new issue to discuss saved. I'm not as warm on it since I have a better understanding of checking the IdleTimeout from middleware.

I'm dropping the request for TouchWithInterval completely.

[jpfluger]

This pull request is old. How about I withdraw this request until v2 comes out and can re-examine? Or leave it here for historical purposes?

As is the case with many gophers, go.mod has forced me to re-address my code-base. (sigh) Which means I'm refreshing my local fork of scs with new commits from master and re-examining if I can merge back into master. I want to but don't know if it's possible - I may have diverged too far from master in my local copy. Once I get my local fork refreshed and tested, I'll post in a new branch echo.

Since this original pull-request, I've come to define session options within a configuration file and feed them into scs. This commit doesn't reflect that.

    "sessionOptions": {
      "domain": "example.com",
      "httpOnly": true,
      "idleTimeoutMinutes": 0,
      "lifetimeMinutes": 1440,
      "name": "session",
      "path": "/",
      "persist": false,
      "secure": false,
      "autoSave": true
    }

[jpfluger]

V2 obsoletes this request. 👍