Add Encoding option to loadjson and savejson

[roslovets]

Hi, I faced a problem with UTF-8 json files containing Russian letters, so I added an Encoding option to loadjson and savejson to successfully work with them. Example:

data = loadjson('file.json', 'Encoding', 'UTF-8');
savejson('', data, 'FileName', 'file.json', 'Encoding', 'UTF-8');

I think this will help many people.

P.S. Thank you for this library!

[fangq]

cool, thank you

just one minor request - before I merge the changes, can you set your editor with a tab width of 8 and align the indentations for the new codes?

thanks, I will merge once the indentations are fixed.

[roslovets]

I have fixed the identation.

[fangq]

thank you, merged!