Fix issue #40. Edited meshing module 2-8 pages.

[francoisdh]

• Solves a few problems described in issue #40,
• improves some code snippets,
• corrects a few typos.

[francoisdh]

Thank you @prudhomm, I have made changes according to your comments.

We should merge this as soon as possible to close issue #40 and have a better documentation online.

We can always improve the documentation later, for example with the options tables.