Merge pull request unidoc#47 from adrg/unipdf-3.6.1

Update unipdf to v3.6.1

Update unipdf dependency to v3.5.0 (unidoc#41)

* Update unipdf to the latest version
* Bump application version to 0.3.1
* Tidy go.mod and go.sum

Update application version to 0.3.0 (unidoc#39)

Merge pull request unidoc#34 from adrg/master

Prepare release of v0.2.0

Merge pull request unidoc#13 from adrg/master

Update unidoc version to v3.0.0-alpha.1 tag