new option to compute char lengths from curvature + removed most unused mesh options

curvature control is ok
divide and conquer algo has been cleaned up

more infrastructure for projection face gui

physical entities can now be defined using a string instead of a number (and
there is a new field $PhysicalNames in the .msh format to keep track of these
strings)

remove elliptic - same as Transfinite with Mesh.Smoothing > 1

- finished volume extrusion
- cleanup ExtrudeParam (plug memory leak + remove unused stuff)
- make netgen the default 3D algo for now (since it actually works)

make explicit regions in extrusions DEPRECATED

cleanup

bidir db: phase 3 -- move all the old geo stuff into Geo/

bidi db: phase 2 -- continued

bidir db: phase 2 -- removed all (well, most of) the old data structures and
algorithms

bidir db: phase 1

- add compatibility syntax for getdp (string~{fexpr})
- add possibility to write/append to files with Printf

merging offscreen rendering from branch

- fix discrete surf (for the 100000th time)
- new Status N command in parser to force mesh status
- create reverse discrete curves

minimize the number of files that include GmshVersion.h: it's annoying to
recompiletoo many files just because the version string changes

moved most OS-dependent functions in OS.cpp

"pure windows" version (without cygwin) is almost there: the solver
interface now works quite nicely using native Windodiows sockets and
the timers work too. There are still some bugs with binary files and
user-created functions in the parser.

added support for empty lists (aa[] = {};) and concatenation of lists
(aa[] += {1,2,3};)

newsl and newll to get next available loop numbers

move yy globals into Gmsh.l

remesh in script

new "Background Mesh" command

removed the STEP parser: it's unusable, it makes the parser bigger,
and it introduces conflicts in the syntax.