fix warnings

[Lagovas]

• added explicit type conversations
• checked comparison of signed/unsigned numbers and added explicit type conversations too
• used #define UNUSED(expr) (void)(expr) to mark variables as unused
• marked function params as void to fix warning: function declaration isn't a prototype
  Fix warnings in C-example #78
  p.s. try to compile hermes + examples again (make clean examples all) and tell which warnings still remain in Fix warnings in C-example #78

[vixentael]

no previous warnings left.

however, I found error message while compiling mid_hermes_ll client, and fixed it.

cd docs/examples/c/mid_hermes_low_level && make
cc -g  ./obj/commands.o  ./obj/credential_store.o  ./obj/data_store.o  ./obj/key_store.o  ./obj/main.o  ./obj/base64.o  ./obj/utils.o -L../../../../build -lsoter -lhermes_mid_hermes_ll -lthemis -o hermes_client_ll
Undefined symbols for architecture x86_64:
  "_cst_time_memcmp", referenced from:
      _mid_hermes_ll_buffer_is_equal in libhermes_mid_hermes_ll.a(mid_hermes_ll_buffer.o)
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[1]: *** [all] Error 1

[vixentael]

😈