Merge pull request input-output-hk#18 from input-output-hk/PR-symboli…

…c-addition

Add support for symbolic TxIn

Merge pull request input-output-hk#17 from input-output-hk/PR-hotfix

One more hotfix

Merge pull request input-output-hk#13 from input-output-hk/PR-observa…

…tions

Add ability to make assertions of the blockchain in DL properties

Fix typo