Merge pull request #379 from olasundell/master

The Makefile is now OSX and Linux aware
Revert "Merge pull request #379 from olasundell/master"

This reverts commit 5ec216800146df0503685e544210ee1daef8d2a1, reversing
changes made to db65f55284a7e45e586defa1dbe280d5f6f2e37d.
Releasing 2.3.0
Preparing 2.3.1 release;
Merge pull request #398 from MuMech/dev

MechJeb 2.3.1 release
Removed revision checking from CompatibilityChecker.
Merge pull request #399 from MuMech/dev

Removed revision checking from CompatibilityChecker, In case we get a KSP 0.24.3 >.>
Maneuverplanner modularization

Maneuvers are now implemented in separate classes.
Each class draws its GUI and has a method to compute the node.
Parameters are inside the Operation object and are not shared anymore.
Implement a (new) combobox utility

Switch maneuver planner selection to the new combobox
Fix steam directory under Linux
Revert "Fix steam directory under Linux"

This reverts commit 8fad790541b2f8af39f913774701e34a2c5ead85.
Simulation ignores engines limited to zero thrust (fixes #395)
Add "Downrange distance" info item to flight recorder.
Turn off bounding boxes upon docking (fixes #386).
Fix empty maneuver box error, make code more resilient
Merge pull request #406 from xytovl/modularManeuverPlanner

Fix empty maneuver box error, make code more resilient
Account for engine spool time in node executor (#407)
Fix #407 for ModuleEngineFX as well.
Fix for ModuleEngineFX for #395
Landing AP course corrections account for engine spool time (#407, #242)