Revision history for Struct-Path
0.84    2019-07-10
        - path() reworked: independent traverse implemented
        - R keys in HASH definitions in no longer supported
0.83    2018-12-15
        - throw correct error for nonrefs in refstack
        - ref() calls reduced a bit
        - regexps supported in hash keys list, R key is deprecated now
0.82    2018-08-15
        - craches fixed for expand out-of range negative array indexes
        - expand-append experimental subopt removed
        - expand lists smoothly for out of range negative indexes (experimental)
        - opts passed to hooks via %_
0.81    2018-01-10
        - path(): resolve negative array indexes in paths
0.80    2017-12-22
        - hash definition format changed, exported subs renamed to avoid ambigouseness
        - path() now works with scalars as is (ref not required)
        - both changes are breaking back compatibility, sorry
0.74    2017-11-20
        - entire thing replacement fixed in spath()
0.73    2017-11-03
        - hooks supported in spath_delta()
        - hooks: set $_ to substructure pointed by current step
        - spelling corrected, cosmetics
0.72    2017-10-15
        - spath(): sane errors for out of range negative array indexes
        - croak if empty path and delete opt passed to spath()
0.71    2017-06-27
        - 'assign' opt to spath() added
        - grow arrays smoothly if 'append' for 'expand' specified in spath() (experimental)
0.70    2017-06-20
        - slist() now returns path-ref pairs in common list
        - spath w opt expand may overwrite existed values now if strict opt permit so
        - croak if nonref passed for structure in spath()
        - output format changed for spath w 'paths' opt
        - 'stack' opt to spath() added
0.65    2017-05-04
        - slist() now also returns references to values
        - refactoring
0.64    2017-03-15
        - is_implicit_step() subroutine added
0.63    2017-02-22
        - docs improved
0.62    2017-01-23
        - 'paths' opt for spath() added (highly experimental)
0.61    2017-01-15
        - discard path if coderef returned false value
        - slist() refactored (~15% faster now)
0.60    2016-12-05
        - regexp match for hash keys specification supported
0.52    2016-11-28
        - Array's items removal fixed (don't fail on out of range indexes in nostrict mode)
0.51    2016-11-27
        - Array's items removal fixed (don't remove items from specified to the end)
0.50    2016-08-30
        - Coderefs as path steps in spath() supported
0.41    2016-08-19
        - spath_delta(): don't return full second path if it's a subset of first one
0.40    2016-08-18
        - spath_delta() appeared
0.33    2016-08-11
        - Dist corrected, tests refactored
0.32    2016-08-05
        - Any thing as a structure accepted by spath() from now on
0.31    2016-08-01
        - Pod corrected
0.30    2016-07-30
        - slist() appeared
0.21    2016-07-07
        - Addressing method in pod described
        - Unsignificant refactoring
0.20    2016-06-28
        - Path structure format changed (hashes definition)
0.12    2016-06-13
        - Pod and dist corrected
0.11    2016-06-12
        - 'expand' opt for spath() implemented
0.10    2016-05-22
        - 'delete' opt for spath() implemented
0.09    2016-05-22
        - Pod and dist corrected, unused code removed
0.08    2016-05-16
        - 'strict' opt appeared
        - tests and dist cleaned up
        - cosmetics
0.04    2016-04-29
        - 'deref' opt for spath() added
0.01    2016-04-27
        - spath() appeared.
        - Draft.