Make Vectors mutable

[jthomperoo]

Part of #148

[codecov-commenter]

Codecov Report

Merging #150 into master will increase coverage by 0.11%.
The diff coverage is 92.59%.

@@            Coverage Diff             @@
##           master     #150      +/-   ##
==========================================
+ Coverage   78.54%   78.65%   +0.11%     
==========================================
  Files          98       98              
  Lines        2978     2985       +7     
  Branches      261      261              
==========================================
+ Hits         2339     2348       +9     
+ Misses        421      419       -2     
  Partials      218      218              

Flag	Coverage Δ
#unittests	78.65% <92.59%> (+0.11%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/shape/aabb.ts	90.32% <ø> (ø)
src/standard/motion/motion_system.ts	0.00% <0.00%> (ø)
src/standard/primitive/primitive_system.ts	89.36% <ø> (ø)
src/standard/sprite/sprite_system.ts	89.79% <ø> (ø)
.../standard/webgl/default_primitive_vertex_shader.ts	27.27% <0.00%> (ø)
...rc/standard/webgl/default_texture_vertex_shader.ts	21.42% <0.00%> (ø)
src/geometry/vector.ts	97.01% <100.00%> (+5.52%)	⬆️
src/shape/ellipse.ts	100.00% <100.00%> (ø)
src/shape/polygon.ts	87.87% <100.00%> (ø)
src/standard/camera/camera.ts	76.19% <100.00%> (-1.09%)	⬇️
... and 14 more