"Intro to QSharp" samples

While the samples serve the purpose of demonstrating the usage of the language, it would be useful to have samples that explicitly demonstrate commonly used QSharp syntax, or even demonstrate more advanced syntax examples, without necessarily producing a useful algorithm. The goal is to make it easy for developers who learn by reading other code to pick up the language quickly.

Some examples:

• within
• Partial application
• Adjoint, Controlled and is Adj + Ctl
• ApplyToEach
• Arrays, both 1D and 2D
• Math, e.g. PowD

Based on contributor discussion.