Remove underscores in method names

[mysticfall]

For now, the be verb is considered as a matcher itself, which enforces other passive verb based matchers to be prefixed with 'be_'.

And even if semantics of presupposition 'in' between a suite definition and an assertation (i.e. be_thrown_in) are quite similar, we have two different set of syntax/APIs to support each.

Ideally, we should be able to write as below, at least :

An_[IllegalStateException] should not be thrown in {
    // (code block)
}

[mysticfall]

As we can now define matchers with the same verb, due to matcher priority support(cf56fcf), it should be possible to remove the 'be_' prefix in be_thrown_in, at least.