Implement `visit` for Log, Csc, Sec and Cot
Add tests and fix a typo
Implement `visit` for inverse functions
Implement `visit` for Symbol

`pi` is used in inverse trignometric functions.
Add tests
Remove redundant checks
Use `eq` to compare `x` against `pi`
Implement `visit` for ATan2 and hyperbolic functions
Add tests
Merge branch 'master' into arb_II
Revert the changes to `visit(Symbol)`
Implement visit for Constant
Remove redundant semicolons
Merge pull request #311 from thilinarmtb/arb_II

Interface Arb II