Added ObjectNav task definition, dataset, metrics, goal sensor.
ObjectGoal Nav Task definition: metrics, goals, sensors with documentations.
ObjectGoal Nav Dataset definition and loading and link for downloading.
Topdown target objects, view points, bounding boxes visualization
Compatible with Benchmark API
Added ObjectNav DDPPO config for a baseline
Made PointNavDataset general enough to be inherited by other Dataset types
Refactored RLEnv to use measures for reward and success to speed up distance calculations
Added mechanism for Measures (Metrics) classes to be depend on other measure. That increased speed and calculation and decrease copy pasta. Speed improvements 2x: from 8 FPS to 15.5 FPS, compare to 40 FPS for PointGoal with same setup.
made SPL dependent on DistanceToGoal
added metrics calc to reset method for SPL and DistanceToGoal

Refactored RLEnv to use measures for reward and success, made SPL dependent on DistToGoal, added metrics calc to reset method

This new feature allows for habitat-api to start a physics-enabled sim

Added interface to calculate geodesic distance to multiple points. The functionality is super convenient for multi target navigation and speed up metrics calculation process.

We still support single point functionality through API and are fully backward compatible.
Switched existing code to multi goal function usage using a single element list.

Version bump, better late than never. That's needed for right package version building.

Habitat sim can now disable sliding. This PR wires up habitat-api with that.

Add DD-PPO to habitat-baselines

fix for #278 reported by @saketd403. and added test for test_observations_to_image

* Added allow_new flag to default config point, added test

* Updated the doc string, converted to module doc string

The contains methods in the three habitat.core.spaces classes (EmptySpace, ActionSpace, and ListSpace) have errors that are described in #271. This pull request fixes those errors, corrects the documentation for the ActionSpace class, and adds a __repr__ to the EmptySpace class.
closes #271

* Made Tensorboard evaluation visualization work for other sensors than RGB
* Added missing dependency

NIT: changed badged order to be consistent with habitat-sim

Added Visual Language Navigation dataset download link

 * Add VLN Task

 * Add reading of Room-to-Room Dataset

 * Add VLN Instruction Sensor

 * Added shortest path follower

 * Added benchmark for Random, ForwardOnly, RandomForward & GoalFollower agent

*  Represent instructions as list of tokens

*  Added vocabulary API to R2R dataset

* Added test coverage measure for habitat-api with codecov

* Added codecov badge

* Removed test that caused failures and wasn't runnning as notebooks were removed from repos

Fix try register for pointnav dataset

`*` messes up with alphabetical ordering in references.

Fix wrong return type of SimulatorTaskAction.step

* Add CUDA path to CI config path

* Fix CI formatting

* Fix bugs in config setup and pause_env condition

* Preserve scene ordering