PR: Add validation to raise exception when fonts are empty or corrupt

[dalthviz]

This is part of an effort to improve the management of errors that cause a Spyder crash when trying to load fonts from the .ttf files in the fonts directory and these are corrupt.

[ccordoba12]

Let's make this a dictionary for clarity, like this:

md5_hashes = {'fontawesome-webfont.ttf': 'a3de2170e4e9df77161ea5d3f31b2668',
              'elusiveicons-webfont.ttf': '207966b04c032d5b873fd595a211582e'}

[ccordoba12]

If we use a dictionary for hashes then this has to be

ttf_hash = md5_hashes.get(ttf_filename, None)
if ttf_hash is not None:
    ...

And yes, please use ttf_hash instead of ttf_hash_code for this variable.

[ccordoba12]

@dalthviz, this looks good to me. I just left a couple of comments to improve readability ;-)

Also, please merge with master to fix the Travis errors.

[ccordoba12]

We need to improve this error message for people that uses QtAwesome on Windows 10. Please rephrase it for something like

"Font at "{0}" appears to be empty. If you are on Windows 10, "
"please read https://support.microsoft.com/en-us/kb/3053676 to "
"know how to prevent Windows from blocking the fonts that come "
"with QtAwesome."

[ccordoba12]

Please format this better:

md5_hashes = {'fontawesome-webfont.ttf':
              'a3de2170e4e9df77161ea5d3f31b2668',
              'elusiveicons-webfont.ttf':
              '207966b04c032d5b873fd595a211582e'}

[ccordoba12]

Thanks @dalthviz, merging now :-)