Implement more options from alter

Here are the modifications available through alter:

Format modification:

• --float switch between DOUBLE and SINGLE precision float
• --endian switch between endian encoddings

Header modification:

• --title TITLE set the title of the file

Date modification:

• --datetime DATETIME set the start date of the file (yyyy-mm-dd hh:mm:ss)

Variable modification:

• --vars XVARS specify which variables should remain (','-delimited)
• --rename RENAME_VAR change the name of a VARIABLE: 'OLD VAR=NEW VAR'
• --var? MODIF_VAR will modify var? ((var*? * val )+ var+?) operations on that VARIABLE name
• --var+? ADD_VAR adds to the VARIABLE
• --var*? MUL_VAR scales the VARIABLE

Time modification:

• --times specify times index
• -f TFROM, --from TFROM specify the first frame included
• -s TEND, --stop TEND specify the last frame included (negative from the end)
• -d TSTEP, --step TSTEP specify the step for the extraction of frames
• --reset-time reset first time to zero by remove t0 to all times
• --T+? ADD_TIME adds to the ATs
• --T*? MUL_TIME scales the ATs

Coordinates modification:

• --sph2ll SPH2LL SPH2LL convert from spherical to longitude-latitude
• --ll2sph LL2SPH LL2SPH convert from longitude-latitude to spherical
• --ll2utm LL2UTM zone info convert from longitude-latitude to UTM (giving XXX will let the script pick the zone otherwise specify zone with number + letter (for example 24S))
• --utm2ll UTM2LL zone info to convert from UTM to longitude-latitude (for example 24S)
• --X+? ADD_X adds to the meshx
• --X*? MUL_X scales the meshx
• --Y+? ADD_Y adds to the meshy
• --Y*? MUL_Y scales the meshy
• --orig ORIG ORIG Origin of coordinates (X_ORIG, Y_ORIG in file)
• --rotate ROTATE Angle of rotation (counter clockwise) to apply in degree
• --rotation-point ROT_PT ROT_PT Point around which to do the rotation
• --center Apply rotation with center of mesh as rotation point
• --proj PROJ Proj using pyproj format (CRSCODE1/CRSCODE2 for example EPSG:4326/EPSG:27561)