1. Parse URDF continuous joint effort/velocity limits

* [Pull request #684](https://github.com/ignitionrobotics/sdformat/pull/684)

1. Add enable_orientation SDF element to imu

* [Pull request #651](https://github.com/ignitionrobotics/sdformat/pull/651)

1. Add a codecheck make target

* [Pull request #682](https://github.com/ignitionrobotics/sdformat/pull/682)

1. Refactor sdf::readXml

* [Pull request #681](https://github.com/ignitionrobotics/sdformat/pull/681)

1. Upgrade cpplint and fix new errors

* [Pull request #680](https://github.com/ignitionrobotics/sdformat/pull/680)

1. BUG: add missing plugin element to include

* [Pull request #675](https://github.com/ignitionrobotics/sdformat/pull/675)

1. Added comment reminder to update functions

* [Pull request #677](https://github.com/ignitionrobotics/sdformat/pull/677)

1. Adds enable_metrics flag to Sensor.

* [Pull request #665](https://github.com/ignitionrobotics/sdformat/pull/665)

1. Add GPS / NavSat sensor to sdf9

* [Pull request #453](https://github.com/ignitionrobotics/sdformat/pull/453)

1. Support parsing elements that are not part of the schema

* [Pull request #638](https://github.com/ignitionrobotics/sdformat/pull/638)

1. Add lightmap to 1.7 spec and PBR material DOM

* [Pull request #429](https://github.com/ignitionrobotics/sdformat/pull/429)

1. Fix urdf link extension tags

* [Pull request #628](https://github.com/ignitionrobotics/sdformat/pull/628)

1. Updated material spec

* [Pull request #644](https://github.com/ignitionrobotics/sdformat/pull/644)

1. Minor fix to Migration guide

* [Pull request #630](https://github.com/ignitionrobotics/sdformat/pull/630)

1. Error: move << operator from .hh to .cc file

* [Pull request #625](https://github.com/ignitionrobotics/sdformat/pull/625)

1. Update build system to allow overriding CXX flags and using clang on Linux

* [Pull request #621](https://github.com/ignitionrobotics/sdformat/pull/621)

1. Add Element::FindElement as an alternative to Element::GetElement

* [Pull request #620](https://github.com/ignitionrobotics/sdformat/pull/620)

1. Add ValidateGraphs methods to Model/World (sdf9)

* [Pull request #602](https://github.com/ignitionrobotics/sdformat/pull/602)

1. Fix ABI break

* [Pull request #605](https://github.com/ignitionrobotics/sdformat/pull/605)

1. Parameter passing prototype

* [Pull request #413](https://github.com/ignitionrobotics/sdformat/pull/413)

1. Port particle scatter ratio param to sdf 1.6

* [Pull request #595](https://github.com/ignitionrobotics/sdformat/pull/595)

1. Making PrintValues() and ToString() able to not print default elements

* [Pull request #575](https://github.com/ignitionrobotics/sdformat/pull/575)

1. Add API for determining if an element was set by the user

* [Pull request #542](https://github.com/ignitionrobotics/sdformat/pull/542)

1. Add GPS / NavSat sensor DOM to sdf9