API adjustment for the STT yielding class to improve friendliness with Ride

[sebastianconcept]

Makes the STT API more consistent with the render:using: and renderUsing: methods seen in Ride's renderer based on STTemplate.

With this change, developers won't need to remember 2 sets of rules for the yield method when used from Ride.

So now this is possible:

<st STT yieldUsing: 'shared/feedback.html' >
<div class="container">
	<h1>Post</h1>
	<st= self render: model>
	<div>
	...

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (e2a3df4) 94.32% compared to head (a04bca9) 97.00%.
Report is 8 commits behind head on master.

❗ Current head a04bca9 differs from pull request most recent head 5b4eb82. Consider uploading reports for the commit 5b4eb82 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #14      +/-   ##
==========================================
+ Coverage   94.32%   97.00%   +2.68%     
==========================================
  Files           5        5              
  Lines        1498     1503       +5     
==========================================
+ Hits         1413     1458      +45     
+ Misses         85       45      -40     

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