Added boundary to read_parameters, macros

Supplement the function read parameters such that it reads initial
values for the variable problem and for the boundary value options
wl,wr,wt and wb.
Defined macros in helper.h:
 1 for no-slip conditions, (NO_SLIP)
 2 for free-slip conditions, or (FREE_SLIP)
 3 for outflow conditions (OUTFLOW)