Added recommended fingering details to guitar chord charts.

As long as we're able to find a fingering, we now show where to place each finger on chord charts. If we find more than one way to play a particular chord chart, we also list these other - usually more difficult - variations on the chart detail page.

New difficulty metric for chord charts.

This is based on the new algorithm described in the previous update, and is used in many places throught the site. The most noticable is in the ranking of chord charts - difficulty, along with number of strings played and position on the neck - are used used to select the first chart to show in search results.

This update should make for a more well rounded selection sorting of results and produce less edge cases of hard-to-play charts showing high in the list.

Filtering of chord charts that are unplayable from search results.

This is accomplished with a new algorithm we have to determine possible ways to play each chord chart (where to place each finger). Our first use of this algorithm is this filtering, but future uses of this will be to show alternatives of where fingers should be placed on the chord charts, as well as updating our chart difficulty metric to be more accurate.