Improve validation Code

[brampf]

The validation routines are currently very limited and do not cover many cases. It should be a piece of cake to implement most if not all of the rule for FITSverify(https://heasarc.gsfc.nasa.gov/docs/software/ftools/fitsverify/):

SEVERE ERROR CONDITIONS

• Mandatory keyword not present or out of order
• Mandatory keyword has wrong datatype or illegal value
• END header keyword is not present
• Sum of table column widths is inconsistent with NAXIS1 value
• BLANK keyword present in image with floating-point datatype
• TNULLn keyword present for floating-point binary table column
• Bit column has non-zero fill bits or is not left adjusted(*)
• ASCII TABLE column contains illegal value inconsistent with TFORMn(*)
• Address to a variable length array not within the data heap(*)
• Extraneous bytes in the FITS file following the last HDU

ERROR CONDITIONS

• Mandatory keyword values not expressed in fixed format
• Mandatory keyword duplicated elsewhere in the header
• Header contains illegal ASCII character (not ASCII 32 - 126)
• Keyword name contains illegal character
• Keyword value field has illegal format
• Value and comment fields not separated by a slash character
• END keyword not filled with blanks in columns 9 - 80
• Reserved keyword with wrong datatype or illegal value
• XTENSION keyword in the primary array
• Column related keyword (TFIELDS, TTYPEn,TFORMn, etc.) in an image
• SIMPLE, EXTEND, or BLOCKED keyword in any extension
• BSCALE, BZERO, BUNIT, BLANK, DATAMAX, DATAMIN keywords in a table
• Table WCS keywords (TCTYPn, TCRPXn, TCRVLn, etc.) in an image
• TDIMn or THEAP keyword in an ASCII table
• TBCOLn keyword in a Binary table
• THEAP keyword in a binary table that has PCOUNT = 0
• XTENSION, TFORMn, TDISPn or TDIMn value contains leading space(s)
• WCSAXES keyword appears after other WCS keywords
• Index of any WCS keyword (CRPIXn, CRVALn, etc.) greater than value of WCSAXES
• Index of any table column descriptor keyword (TTYPEn, TFORMn, etc.) greater than value of TFIELDS
• TSCALn or TZEROn present for an ASCII, logical, or Bit column
• TDISPn value is inconsistent with the column datatype
• Length of a variable length array greater than the maximum length as given by the TFORMn keyword
• ASCII table floating-point column value does not have decimal point(*)
• ASCII table numeric column value has embedded space character
• Logical column contains illegal value not equal to 'T', 'F', or 0(*)
• Character string column contains non-ASCII text character(*)
• Header fill bytes not all blanks (**)
• Data fill bytes not all blanks in ASCII tables or all zeros in any other type of HDU (**)
• Gaps between defined ASCII table columns contain characters with ASCII value > 127 (**)

WARNING CONDITIONS

• SIMPLE = F
• Presence of deprecated keywords BLOCKED or EPOCH
• 2 HDUs have identical EXTNAME and EXTVER values
• BSCALE or TSCALn value = 0.
• BLANK OR TNULLn value exceeds the legal range
• TFORMn has 'rAw' format and r is not a multiple of w
• DATE = 'dd/mm/yy' and yy is less than 10 (Y2K problem??)
• Index of any WCS keyword (CRPIXn, CRVALn, etc.) greater than value of NAXIS, if the WCSAXES keyword is not present
• Duplicated keyword (except COMMENT, HISTORY, blank, etc.)
• Column name (TTYPEn) does not exist or contains characters other than letter, digit and underscore
• Binary table has PCOUNT > 0, but no variable-length array columns
• Calculated checksum inconsistent with CHECKSUM or DATASUM keyword(***)
• The HEASARC long string keyword convention is used without the recommended LONGSTRN keyword (****)

(*) only checked when "testdata" is 'Yes'
(**) only checked when "testdata" and "testfill" are 'Yes'
(***) only checked when "testdata" and "tchksum" are 'Yes'
(****) only checked when the "heasarc" is 'Yes'

Every HDU in the FITS file is checked in turn until the end of file is detected.