Add check for if constraint indendation

[wilzbach]

So I rewrote #394 to use the tokens stream instead 🎉
In the beginning I save for every line its indendation level and whether it starts with the if token.

As Phobos has been unified in February, only a few matches can be observed, but all are regressions :)

std/conv.d(5710:47)[warn]: If constraints should have the same indentation as the function
std/numeric.d(2613:9)[warn]: If constraints should have the same indentation as the function
std/numeric.d(2670:9)[warn]: If constraints should have the same indentation as the function
std/digest/crc.d(163:33)[warn]: If constraints should have the same indentation as the function
std/experimental/allocator/common.d(549:13)[warn]: If constraints should have the same indentation as the function
std/algorithm/searching.d(1323:9)[warn]: If constraints should have the same indentation as the function
std/algorithm/searching.d(1336:9)[warn]: If constraints should have the same indentation as the function
std/algorithm/searching.d(3365:9)[warn]: If constraints should have the same indentation as the function
std/algorithm/searching.d(3382:9)[warn]: If constraints should have the same indentation as the function
std/concurrency.d(465:38)[warn]: If constraints should have the same indentation as the function
std/concurrency.d(490:44)[warn]: If constraints should have the same indentation as the function
std/concurrency.d(499:60)[warn]: If constraints should have the same indentation as the function
std/range/package.d(7443:9)[warn]: If constraints should have the same indentation as the function
std/range/package.d(7449:9)[warn]: If constraints should have the same indentation as the function

[wilzbach]

Rebased to master

[wilzbach]

Rebased this to master, so it should finally be ready & mergable :)

[wilzbach]

Rebased to the new dscanner layout and for the 0.5.0 inclusion.