Divided various get...() string functions into get...() and append...()
functions.  The get...() ones clear the string first, whereas the
append...() ones don't.
Renamed new append...() string functions to read...() functions.
read...() functions do not clear the output string whereas get...()
functions do.
Documented the difference between the get...() and read...() functions
in dsl-pa-dsl-pa.h.
Added read...() and get...() variants for get_fixed, get_ifixed,
get_bool, get_int, get_uint, get_float and get_sci_float.
Fixed tabs to spaces etc.