F_SAC: Manipulating SAC files

Read/Write/Change data and header from SAC formatted files.

FREAD_SAC reads a IRIS/SAC file in specified machine format, and returns in 2 types: 1) time vector, data vector, and header structure; or 2) a whole structure variable whose fields are time, data, and header separately. The field names of a SAC structure variable correspond to standard IRIS SAC header version 6.0 field names, in lower case.
FWRITE_SAC reads a SAC structure variable (which can be produced by your own or FREAD_SAC), completes the missing headers, and/or write it to a file in specified machine format.