document '--enable-debug' configure flag
html: larger width in CSS and tiny clarification.
HTML: document 'Double precision' file extensions and build instructions.
NSIS: use 'tasklist' instead of 'qprocess'.
build-nsi: fine tune unmangle paths when running on MinGW
NSIS: tell msys2 users that they have to build with a 32bit nsis.
nsis: installer updates
release notes: tell that the Windows installer can be run on non-admin users