Fixes Issues #189 and #191

For fixing #189, we are supporting builtin CJK fonts now (CJK = China, Japan, Korea). This should lead to correctly generated pixmaps for documents using these languages. This change has consequences for our binary file size: it will now range between 8 and 10 MB, depending on the OS.

Issue #191 occurred when setting the contents of an annotation. Certain values had been incorrectly de-referenced in PyMuPDF's C-level.

Since the previous release, we are also generating wheels for Python 3.7 in OS Linux and Mac OS.