Description

Fully documented the position_heading_publisher_node.py
also explained the modular template that it uses for future position/heading filters

Fixes #231

Type of change

Name change from Position_Publisher_Node to position_heading_publisher_node in each file
documentation of the same node AND documentation update in the old gps_example.md

[x] My code follows the style guidelines of this project
[x] I have performed a self-review of my own code
[x] I have commented my code, particularly in hard-to-understand areas
[x] I have made corresponding changes to the documentation
[x] My changes generate no new warnings
[x] I have added tests that prove my fix is effective or that my feature works (might be obsolete with CI later on)
[x] New and existing unit tests pass locally with my changes (might be obsolete with CI later on)

Metric	Value
Avg. driving score	0.002458
Avg. route completion	38.845
Avg. infraction penalty	0.000191
Collisions with pedestrians	0.164
Collisions with vehicles	7.718
Collisions with layout	4.434
Red lights infractions	0.0
Stop sign infractions	0.328
Off-road infractions	0.192
Route deviations	0.164
Route timeouts	0.0
Agent blocked	0.164
Yield emergency vehicles infractions	0.0
Scenario timeouts	0.0
Min speed infractions	0.328