Fix Sign-Conversion warnings in library and test code (#214)

* JuliaStrings#169 turn on sign-conversion warnings

Signed-off-by: Mike Glorioso <mike.glorioso@gmail.com>

* JuliaStrings#169 fix sign-conversion warnings for utf8proc.c

fix sign-converstion warnings for utf8proc_iterate
uc requires at most 21 bits to identify a unicode codepoint, so there is no need for it to be unsigned
multiple locations use, modify, or store uc with a signed value
the only exception is line 137 where uc is compared with an unsigned value

fix sign-converstion warnings for utf8proc_tolower, utf8proc_toupper, utf8proc_totitle
all three methods have sign conversion warnings when calling seqindex_decode_index
seqindex_decode_index uses the passed value as an index to an array utf8proc_sequences
as utf8proc_sequences is hard-coded and smaller than 2^31 - 1 we can safely cast to unsigned

fix sign-converstion warnings for utf8proc_decompose_char
lines with this warning use the defined function utf8proc_decompose_lump
in the function, a hardcoded unsigned value (1<<12) is complemented then cast as a signed value
as the intent is to remove the 12th bit flag from options, a signed value, and explicit cast is safe

fix sign-conversion warnings for utf8proc_map_custom
result is declared as signed, but is only expected to contain values between 0 and 4
sizeof returns an unsigned value. result must be cast to unsigned

Signed-off-by: Mike Glorioso <mike.glorioso@gmail.com>

* JuliaStrings#169 fix sign-conversion warnings for test/*

fix sign-conversion warnings for test/tests.c encode
change type for d to match return value of utf8proc_encode_char

fix sign-conversion warnings for test/graphemetest.c checkline
si, i, and j are unsigned size types, utf8proc_map and utf8proc_iterate accept and return signed size types
utf8proc_map treats negative strlen values as 0. the strlen used by the test must be similarly limited
utf8proc_iterate treats negative strlen values as 4 which will be less than the unsigned size
fix unused-but-set-variable warning by checking the glen value

fix sign-conversion warnings for test/case.c main
the if block ensures that tested codepoint fits in wint_t, but needs to include u and l as well
c, u, and l can be safely cast to wint_t

fix sign-conversion warnings for test/iterate.c
all values used for len are below 8, so an explicit cast is safe
updated types for more portable test code

fix sign-conversion warnings for test/printproperty.c main
change type of c to signed to resolve all sign-converstion warnings.
replace sscanf(... &c) wiht sscanf(... &x) followed by explicit sign converstion

Signed-off-by: Mike Glorioso <mike.glorioso@gmail.com>

Makefile

@@ -11,7 +11,7 @@ PERL=perl
 CFLAGS ?= -O2
 PICFLAG = -fPIC
 C99FLAG = -std=c99
-WCFLAGS = -Wall -Wextra -pedantic
+WCFLAGS = -Wsign-conversion -Wall -Wextra -pedantic
 UCFLAGS = $(CPPFLAGS) $(CFLAGS) $(PICFLAG) $(C99FLAG) $(WCFLAGS) -DUTF8PROC_EXPORTS $(UTF8PROC_DEFINES)
 LDFLAG_SHARED = -shared
 SOFLAG = -Wl,-soname