Support for storage array delete ops

[sifislag]

Add some support for array delete operations.
Output relation is the following:

/**
  An `array` is deleted by setting its length to zero in `sstore` and then erasing all its contents in a following `loop`. 
*/
.decl ArrayDeleteOp(sstore: Statement, loop: Block, array: StorageConstruct)

Also added some cases in InductionVariableUpperBoundVar, and better documented the rules.

[github-actions]

Test Results (Souffle 2.3)

55 tests  ±0   55 ✅ ±0   32m 53s ⏱️ +28s
 1 suites ±0    0 💤 ±0 
 1 files   ±0    0 ❌ ±0 

Results for commit ce5172a. ± Comparison against base commit 09d12c2.

[github-actions]

Test Results (Souffle 2.4)

55 tests  ±0   55 ✅ ±0   33m 33s ⏱️ -31s
 1 suites ±0    0 💤 ±0 
 1 files   ±0    0 ❌ ±0 

Results for commit ce5172a. ± Comparison against base commit 09d12c2.