Subplots - Subplotting made easy

A wrapper for subplots() which allows declaring the subplot grid only once, and enables easily access to the grid's axes.

A subplot handler, to be used instead of subplot(). Main features:
- Subplot grid is defined once, instead of at each axis creation.
- Option to auto-determine grid dimensions by giving only the total
number of axes.
- Active axis can be specified in several ways:
1. "Flat" index
2. Sub-index
3. Determined automatically according to axis order
- The axis handles are saved to an array for later access.