Backticked function names in tests

[voddan]

The function names section permits using underscores in test function names to ease reading: @Test fun pop_emptyStack()

I propose:

1. Permitting the usage of backticked test function names together with spaces for separating logical components of the name: @Test fun `pop emptyStack`()
2. Recommending either the underscored naming or the backtick-spaced as a preferred way of naming for test functions

[JakeWharton]

This used to be allowed, but since the dex file format forbids spaces it didn't make sense to allow it with heavy caveats which can't be enforced by a tool.

Perhaps if the dex format gets changed it can be reconsidered.