Merge pull request #76 from dimagi/cz

add SafeSaveDocument base class
use an Exception subclass in excel->json reader
Merge pull request #77 from dimagi/better-error

use an Exception subclass in excel->json reader
add (backported) make_template_fragment_key
Merge pull request #78 from dimagi/cache

add (backported) make_template_fragment_key
Merge pull request #79 from dimagi/cz

add safe_delete
add utility function for dealing with Resource Conflicts when saving documents
changes based on PR
Merge pull request #80 from dimagi/apply-update

add utility function for dealing with Resource Conflicts when saving doc...
add create_unique_filter and tests

(is there a better existing way to do this? i couldn't find one)
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dead comment
Merge pull request #81 from dimagi/unique-filter

add create_unique_filter and tests
use sets for uniqueness (reduces computation time)
add json_format_date
Merge pull request #82 from dimagi/unique-filter

use sets for uniqueness (reduces computation time)
Merge pull request #83 from dimagi/format-date

add json_format_date
make memoized support additional cases
Merge branch 'master' into droos
Merge pull request #84 from dimagi/droos

change to memoized decorator