move delete_all to relation

[shmax]

Removing the concept of passing conditions to Model:

• moved delete_all to Relation
• changed Table::delete to work more similarly to Table::find.

Since it now chains off of Where like anything else, I was able to remove all the tests that were exercising different args delete_all.

[codecov]

Codecov Report

Merging #94 (2aba4ac) into master (904ca1f) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master      #94      +/-   ##
============================================
+ Coverage     98.31%   98.35%   +0.04%     
+ Complexity      964      960       -4     
============================================
  Files            34       34              
  Lines          2372     2369       -3     
============================================
- Hits           2332     2330       -2     
+ Misses           40       39       -1     

Files Changed	Coverage Δ
lib/SQLBuilder.php	100.00% <ø> (ø)
lib/Model.php	99.76% <100.00%> (+0.22%)	⬆️
lib/Relation.php	100.00% <100.00%> (ø)
lib/Table.php	99.06% <100.00%> (ø)

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