Change prime to "first composant"

This was already discussed. Some 1s are written like ' but in this case it's a composant number and not a derivative
Correct function description in definition 8.57

Omega is not in R^n but a subset as written in Struwe's script p. 177. This is a mistake in the notes.
The function described is from Omega to R^l
Correction to definition 8.57

df(x0) is a vector composed from the differentials of each component f^i of f
Correct dimension

g maps to R^2 and not R^3
Merge pull request #60 from pec0ra/patch-1

Small corrections in the two last subchapters