Fixed reference errors.

Removed gitpod link in README.

Refined int-tree to avoid confustion about mask value vs. mask bits.

Updated PDFs with feedback up to 12/31/2024

Worked around cref issue after TeXLive upgrade, changed from cref to ref for now

debugging cref issue - force label of subsection type

debugging cref issue

Debugging cref issue - crefname{section}

debugging issue related to cref

debugging extra endcsname issue

Fixed a typo of range [a, b)

Comment out the cover page image

Fixed incorrect prefix/mask in figure 6.6(b)

Updated action to v4

Add the preface of the 2nd edition to README