Implement ISO week date format

New %timestamp-decode-iso-week function and supporting
FORMAT-TIMESTRING changes, including an +iso-week-format+ constant.
fix encode/decode incongruence caused by changing decode-timestamp
add iso week date formatting tests
Update documentation with ISO week date options
Merge pull request #5 from felideon/iso-week-date

Implement support for ISO week dates
treat 02/29 like 02/28 in timestamp-full-year-difference
Merge branch 'master' of github.com:dlowe-net/local-time
Merge pull request #6 from mcna/master

Bug fix for timestamp-whole-year difference
Fixed compiler notes and an incompatibility with asdf3
New version of local-time 1.0.4