Bland-Altman and Correlation Plot

Added coefficient of correlation and coefficient of determination options as suggested by Tomasz Czernuszewicz.

Two SSE and RMSE values are now available: for the linear regression on the correlation plot, and for the difference between paired data on the Bland-Altman plot.
Added example multiple Bland-Altman plots in a single figure.
Improved error messages.

Fixed non-parametric comparison to use signrank instead of ranked sum (credits to Smilla for bringing this issue to my attention).
Also includes minor comment improvements.

Changes include:
- Explicit support (including demo) for correlation analysis only with correlationPlot.m.
- Improved support for titles and legend with multiple analyses on a figure.
- Legend on/off.
- Text remains on plots when resized.

Corrected code typos as reported by Andrew Stephens. Thank you, Andrew.

Addressed bugs indicated by Rik Wisselink and Cheryl Sital in version 1.7.

Added support for data containing nan values.

Minor comment updates.

Corrected bug with wrong labelling of Bland-Altman x-axis when using data1Mode = 'Truth'.

Added mynum2str and fixed bug with equation option not showing intercept default. Thank you everyone for your comments.

New feature include:
- Parameter-value pair input arguments (incompatible with V1.1).
- Gaussian/non-parametric statistics (including warning for data that may violate this assumption)
- Absolute/relative differences
- Correction of SSE calculation

Added more default colours and the option to specify colours both as code characters and RGB table. See the demo file for and example.