Changes to improve readability, function types and merged clif_skillup and clif_guild_skillup

Added is_even and is_odd to utils.h

Changed types in clif.c:
bool clif_setip -> map:ip_set, map: char_ip_set changed as well
bool clif_setbindip
bool clif_send
bool clif_spawn
void clif_homskillinfoblock
bool clif_sub_guild_invite

clif_disp_onlyself replaced as a macro (should clif_feel_hate_reset and clif_mission_info be replace as well?)
clif_viewequip_fail replaced as a macro
Merged clif_skillup and clif_guild_skillup as they were related to the same packet
Added packet_len() values in clif_updatestatus