Add keywords to logs

[libertylocked]

keywords is a string that gets emitted in LogRecordAdded event. Database indexing services that listen for contract events can store the keywords along with the hash of a file, allowing record searching by keywords.

[buendiadas]

LGTM overall

Open question, no PR blocker wouldn't it be interesting to have keywords indexed as well? So I could look for a type of data directly without making any intermediate DB.

[libertylocked]

@buendiadas posibly, but keywords right now aren't editable after adding. also the keywords aren't attested.

edit: actually, i don't think indexed works with string. it may be possible to use indexed bytes32 instead of string if we limit the keywords to 256 characters

[codecov-io]

Codecov Report

Merging #22 into master will not change coverage. The diff coverage is 100%.

@@           Coverage Diff           @@
##           master      #22   +/-   ##
=======================================
  Coverage   96.33%   96.33%           
=======================================
  Files           4        4           
  Lines         109      109           
  Branches       22       22           
=======================================
  Hits          105      105           
  Misses          4        4

Impacted Files	Coverage Δ
contracts/LinniaRecords.sol	98.14% <100%> (ø)	:arrow_up:

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[buendiadas]

@libertylocked I don't think it can be done with string, sth like bytes.

Even something like a namehash could be interesting (could enable meta inheritance, and a bit extra privacy)

Food for thoughts!