@espy and conditional statement #106

@espy does not, and should not support conditional statements (if, for, while). However:

1. it should support the syntax local ☼myvar
2. the doc should present the pattern

if cond
    myvar = something
else
    myvar = somethingelse
end
local ☼myvar

3. Update the code of ElementCostAndConstraints with this pattern.