ck_rhs: Introduce ck_rhs_set_load_factor() to change the load factor.

The default value is still 50, but that may be revisited later.
Also, pre-calculate the max number of entries before growing, toi avoid
having to do it at each insert.

doc/ck_rhs_set_load_factor

@@ -0,0 +1,72 @@
+.\"
+.\" Copyright 2015 Olivier Houchard.
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+.Dd May 16, 2015
+.Dt CK_RHS_SET_LOAD_FACTOR 3
+.Sh NAME
+.Nm ck_rhs_set_load_factor
+.Nd change the hash set load factor
+.Sh LIBRARY
+Concurrency Kit (libck, \-lck)
+.Sh SYNOPSIS
+.In ck_rhs.h
+.Ft bool
+.Fn ck_rhs_set_load_factor "ck_rhs_t *hs" "unsigned int load_factor"
+.Sh DESCRIPTION
+The
+.Fn ck_rhs_set_load_factor 3
+function will change the load factor of the hash set. The hash set will grow if it is load_factor% filled.
+.Ed
+.Sh RETURN VALUES
+.Fn ck_rhs_set_load_factor 3
+returns true on success, or false if either the load factor is invalid (0 or > 100), or if growing was required, but failed.
+.Sh ERRORS
+Behavior is undefined if
+.Fa hs
+is uninitialized. Behavior is
+undefined if this function is called by a non-writer
+thread.
+.Sh SEE ALSO
+.Xr ck_rhs_init 3 ,
+.Xr ck_rhs_move 3 ,
+.Xr ck_rhs_destroy 3 ,
+.Xr CK_RHS_HASH 3 ,
+.Xr ck_rhs_iterator_init 3 ,
+.Xr ck_rhs_next 3 ,
+.Xr ck_rhs_get 3 ,
+.Xr ck_rhs_put 3 ,
+.Xr ck_rhs_put_unique 3 ,
+.Xr ck_rhs_set 3 ,
+.Xr ck_rhs_fas 3 ,
+.Xr ck_rhs_remove 3 ,
+.Xr ck_rhs_grow 3 ,
+.Xr ck_rhs_gc 3 ,
+.Xr ck_rhs_rebuild 3 ,
+.Xr ck_rhs_count 3 ,
+.Xr ck_rhs_reset 3 ,
+.Xr ck_rhs_reset_size 3
+.Pp
+Additional information available at http://concurrencykit.org/