update docs to Taal and fix typos

[ranocha]

This updates the docs to Taal (elixirs instead of parameter files etc.). I've also left a TODO note for you, @sloede.

[sloede]

LGTM. Also, I didn't find the todo note you left for me, so I'd go as far as to say that it looks excellent to me ;-)

[sloede]

Oops, I didn't mean to approve just yet... Please have a look at my comments first 😬

[codecov]

Codecov Report

Merging #298 into dev will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev     #298   +/-   ##
=======================================
  Coverage   87.79%   87.79%           
=======================================
  Files          79       79           
  Lines       13141    13141           
=======================================
  Hits        11537    11537           
  Misses       1604     1604           

Flag	Coverage Δ
unittests	87.79% <ø> (ø)

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Impacted Files	Coverage Δ
src/Trixi.jl	100.00% <ø> (ø)
src/equations/1d/linear_scalar_advection.jl	79.10% <ø> (ø)
src/equations/2d/linear_scalar_advection.jl	76.74% <ø> (ø)
src/equations/3d/linear_scalar_advection.jl	75.43% <ø> (ø)
src/run.jl	93.64% <ø> (ø)

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