Splayout

* FDTD regions can be defined with z_min&z_max.

* Support vertical sources and monitors.
* 2D index monitor regions and 2D field monitor regions.
* Support custom source distribution.

* Able to set items enable/disable for those saved in list or numpy.ndarray.
* Optimize pixels regions for faster creating.

* Able to get eigenmode distribution from mode monitor.
* Enhance reliability for executing simulations.
* Figures can be shown when it is required in the inverse design regions.
* Able to get magnetic field intensity from field regions.
* Able to get power of the sources with specific wavelengths.

* Alternative show for figure plot.
* Able to reset targets for adjoint methods.
* Add use('AGG') for matplotlib.
* Enhance reliability for executing simulations.

* Able to save the fdtdfile without changing working path.
* Able to create inexistent folders to save figures.