emit_first matcher now catches value differences

emit_first matcher in versions previous to 0.3.1 (it was introduced in 0.2.0) would effectively only compare number of emitted items to expectation, not their actual value. This is now rectified.

Presentation improvements

• emit_exactly presents diff
• unexpectedly emitted errors now include tracebacks

emit_first matcher

emit_first matcher will match against the first element(s) an observable emits.

emit_include matcher

emit_include matcher will stay subscribed to an observable until it has fulfilled a set of matches.

emit_exactly matcher

Initial project release. Now supports matching the exact sequence emitted by an observable.