E-book viewer: When using the tap and hold gesture on a touchscreen, allow lookup  of the word currently under the finger in the dictionary or online. Fixes #1318242 [Enhancement: allow text select on Windows Tablet, perhaps with stylus](https://bugs.launchpad.net/calibre/+bug/1318242)
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Make word under cursor detection more robust
Change the demo link in the README.md

The demo link (https://calibre-ebook.com/demo) present in the README.md threw a certificate error. This modification makes the URL use the HTTP protocol to avoid this issue.
Merge branch 'patch-1' of https://github.com/aymericbeaumet/calibre