Add the possibility to specify the mesh format

[Nicogene]

It fixes #61

For now the supported are:

• stl_binary
• stl_ascii
  - neutral
• step

cc @pillai-s @traversaro @pattacini

[traversaro]

There is any Creo doc explaining what neutral is?

[Nicogene]

There is any Creo doc explaining what neutral is?

Not sure, probably yes but not public

Cc'ing @fiorisi @Mick3Lozzo maybe knows about it

[fiorisi]

There is any Creo doc explaining what neutral is?

Not sure, probably yes but not public

Cc'ing @fiorisi @Mick3Lozzo maybe knows about it

If I am not mistaken, Neutral files should be used to exchange models between different releases of Creo.
Not sure if other CAD softwares can open this kind of files, but for example can be opened with eDrawings.

[Nicogene]

There is any Creo doc explaining what neutral is?

Not sure, probably yes but not public
Cc'ing @fiorisi @Mick3Lozzo maybe knows about it

If I am not mistaken, Neutral files should be used to exchange models between different releases of Creo. Not sure if other CAD softwares can open this kind of files, but for example can be opened with eDrawings.

In this sense I will remove then the possibility to export meshes as neutral since it seems not a use case useful