Update operators syntax

[JPDSousa]

Use a more SQL-like syntax for update operators:

• x INCREMENT/DECREMENT y -> x = x +/- y
  • x is the name of the column
  • y is the value to increment/decrement
  • Consider * and / as (invalid) operators
  • Do not consider more than 2 clauses (i.e. a + b)
• x ASSIGN y -> x = y
  • x is the name of the column
  • y is the value to assign to x
    • Alternatively, y could the name of another column
• x ENABLE/DISABLE -> x = True/False
  • x is the name of the column
  • True/False are constants