[feature#36] support for transactions with mongoDB 4.0 (#37)

Merge pull request #33 from kaiso/feature/#31

Feature/#31

Update README.md

[misc] add comments

Merge pull request #24 from kaiso/hotfix/#21

Hotfix/#21

Merge branch 'support/hotfix/#21' into support/1.X.X

Merge pull request #22 from kaiso/support/hotfix/#21

[bug][#21] child document is not loaded when the joinproperty and the…

[fix] do not override attribute when can not fetch child collection

Merge pull request #20 from kaiso/support/feature/#14

[fix] do not override attribute when can not fetch child collection

prepare 2.0.0 release