Update to swift 4

Fix crash when no items in graph data.

Fix crash when no items in graph data.

Merge pull request collectiveidea#89 from collectiveidea/remove-bg-queue

Remove bg queue

Remove creation of Static Attributes on bounds change.

Merge pull request collectiveidea#74 from collectiveidea/fix-backgrou…

…nding-crash

Tally up the number of background requests going on and just update t…

Merge pull request collectiveidea#69 from collectiveidea/add-images-r…

…eadme

Fix path to images

Fix: Check for NaN!

Merge pull request collectiveidea#60 from collectiveidea/bug-xlabels-…

…incorrect-values

Adjusted calculation of xLabel text.

Merge pull request collectiveidea#59 from collectiveidea/fix-xOffset

Take into account the min value when plotting the xVals.