Add dxf header value reading

[Dubstar_04]

Read relevant dxf values from header

$ACADMAINTVER
$ACADVER
$ANGBASE
$ANGDIR
$ATTMODE
$AUNITS
$AUPREC
$CECOLOR
$CELTSCALE
$CELTYPE
$CELWEIGHT
$CPSNID
$CEPSNTYPE
$CHAMFERA
$CHAMFERB
$CHAMFERC
$CHAMFERD
$CLAYER
$CMLJUST
$CMLSCALE
$CMLSTYLE
$DIMADEC
$DIMALT
$DIMALTD
$DIMALTF
$DIMALTRND
$DIMALTTD
$DIMALTTZ
$DIMALTU
$DIMALTZ
$DIMAPOST
$DIMASO
$DIMASZ
$DIMATFIT
$DIMAUNIT
$DIMAZIN
$DIMBLK
$DIMBLK1
$DIMBLK2
$DIMCEN
$DIMCLRD
$DIMCLRE
$DIMCLRT
$DIMDEC
$DIMDLE
$DIMDLI
$DIMDSEP
$DIMEXE
$DIMEXO
$DIMFAC
$DIMGAP
$DIMJUST
$DIMLDRBLK
$DIMLFAC
$DIMLIM
$DIMLUNIT
$DIMLWD
$DIMLWE
$DIMPOST
$DIMRND
$DIMSAH
$DIMSCALE
$DIMSD1
$DIMSD2
$DIMSE1
$DIMSE2
$DIMSHO
$DIMSOXD
$DIMSTYLE
$DIMTAD
$DIMTDEC
$DIMTFAC
$DIMTIH
$DIMTIX
$DIMTM
$DIMTMOVE
$DIMTOFL
$DIMTOH
$DIMTOL
$DIMTOLJ
$DIMTP
$DIMTSZ
$DIMTVP
$DIMTXSTY
$DIMTXT
$DIMTZIN
$DIMUPT
$DIMZIN
$DISPSILH
$DWGCODEPAGE
$ELEVATION
$ENDCAPS
$EXTMAX
$EXTMIN
$EXTNAMES
$FILLETRAD
$FILLMODE
$FINGERPRINTGUID
$HANDSEED
$HYPERLINKBASE
$INSBASE
$INSUNITS
$JOINSTYLE
$LIMCHECK
$LIMMAX
$LIMMIN
$LTSCALE
$LUNITS
$LUPREC
$LWDISPLAY
$MAXACTVP
$MEASUREMENT
$MENU
$MIRRTEXT
$ORTHOMODE
$PDMODE
$PDSIZE
$PELEVATION
$PEXTMAX
$PEXTMIN
$PINSBASE
$PLIMCHECK
$PLIMMAX
$PLIMMIN
$PLINEGEN
$PLINEWID
$PROXYGRAPHICS
$PSLTSCALE
$PSTYLEMODE
$PSVPSCALE
$PUCSBASE
$PUCSNAME
$PUCSORG
$PUCSORGBACK
$PUCSORGBOTTOM
$PUCSORGFRONT
$PUCSORGLEFT
$PUCSORGRIGHT
$PUCSORGTOP
$PUCSORTHOREF
$PUCSORTHOVIEW
$PUCSXDIR
$PUCSYDIR
$QTEXTMODE
$REGENMODE
$SHADEDGE
$SHADEDIF
$SKETCHINC
$SKPOLY
$SPLFRAME
$SPLINESEGS
$SPLINETYPE
$SURFTAB1
$SURFTAB2
$SURFTYPE
$SURFU
$SURFV
$TDCREATE
$TDINDWG
$TDUCREATE
$TDUPDATE
$TDUSRTIMER
$TDUUPDATE
$TEXTSIZE
$TEXTSTYLE
$THICKNESS
$TILEMODE
$TRACEWID
$TREEDEPTH
$UCSBASE
$UCSNAME
$UCSORG
$UCSORGBACK
$UCSORGBOTTOM
$UCSORGFRONT
$UCSORGLEFT
$UCSORGRIGHT
$UCSORGTOP
$UCSORTHOREF
$UCSORTHOVIEW
$UCSXDIR
$UCSYDIR
$UNITMODE
$USERI1 - 5
$USERR1 - 5
$USRTIMER
$VERSIONGUID
$VISRETAIN
$WORLDVIEW
$XEDIT