[Perf] Minor optimization (since mutations can be very frequent in some pages)
[Fix] Use capturing phase to bind event so that it's handled even if supressed by some other code
[Minor] Added comments
[Perf] perf improvement
[Minor] minor change
[Fix] return body if no other element found to scroll. Fixes #7
[Minor] changed description
[Minor] changed comment to show that 'false' is supported as well
[Refactor] Move back to using the central mutation observer
[Perf] Commented out call to `canIgnoreAllChildlistNodes` for now (since we stop mutation observer before making dom changes anyway)
[Perf/Refactor] Many perf changes related to mod_CUsMgr and mod_filterCUs + etc

[Perf] Much better handling of DOM mutations. DOM changes are handled faster now, while causing less performance hit than before. This is due to having multipe DOM mutation handlers which selectively target important elemetnts/events (i.e. scrollHeight change for now) for handing DOM mutations.
[Perf] Major perf improvements for filtering (more work needed for filtering on heavy sites on slower machines, because of continuous DOM mutations especially while filtering)
[Feature] mod_filterCUs: (This is related to the above point) To a CU being removed by filtering, we now only apply a class, rather than removing elements from the CUs array. $CUsArray renamed to CUs_main (this contains only the filtered CUs) and anothe called _CUs_all added
[Perf] `new Date()` replaced by `Date.now()`
[Refactor] `lastSelectedCUTime` renamed more aptly to `time_lastCUSelectOrDeselect`
[Perf] In function `isCUInvisible`: eliminate usage of jQuery's `is(':visible')` which is seemingly very slow. Also no longer checking for inner elements, since its not needed.
[Refactor/Perf] Convert `buildCUsAroundCentralElement` to an outer function
setelectNext/selectPrev/selectFirst/selectLast methods modified accordingly. Function `filterCUsArray` renamed to `applyFiltering`
[Perf] Misc minor perf improvements
[Refactor] Misc minor refactoring
[Refactor] updateCUsAndRelatedState quality improved. No longer needs an argument to indicate the reason for it being invoked. Code flow for Filtering separated from this. Also longer need the flag `onDomChangeORWindowResize` in this function or elsewhere in the code.