Clarify the command request rejection callback API

[dmitrykuzmin]

This PR resolves #6.

With the current imlementation, it seems that the onRejection callback for a command request will be run once the command leads to a business rejection. But in reality that's not the case.

The callback will be invoked if and only if the passed command cannot bypass the command bus filters due to a business rejection (created and thrown by a filter). It is a valid use-case in our system for e.g. security.

This PR thus renames the callback to onImmediateRejection and adjusts the corresponding doc.

The "ordinary" (thrown by handler methods) rejections can be tracked using the observe(...) method of CommandRequest.

Library version advances to 1.5.25.

[dmitrykuzmin]

@armiol PTAL.

I couldn't come up with an obviously better term than onImmediateRejection. I can propose something like onFilterRejection, onExecutionDenied, onDeskRejection (a term with similar meaning but it sounds a bit strange in this context).

The build will pass once core-java#1295 is merged.

[armiol]

@dmitrykuzmin LGTM with a single comment to address.

[codecov]

Codecov Report

Merging #151 into master will decrease coverage by 0.36%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master     #151      +/-   ##
============================================
- Coverage     62.16%   61.79%   -0.37%     
  Complexity      178      178              
============================================
  Files            87       88       +1     
  Lines          2175     2188      +13     
  Branches         38       40       +2     
============================================
  Hits           1352     1352              
- Misses          814      827      +13     
  Partials          9        9              

[dmitrykuzmin]

The missing coverage are either lines fully covered by the integration tests, or the integration tests themselves. So I'm merging the PR.