[z2099] Fix some problems detected by static code analysis

(based on commit [12143] - 45e0f8c)

(based on commit [s1718] - 7c37a7b)
[z2100] Add support to link summoned npcs with following

Thanks to crackm for insisting that this needs a core change and testing

(based on commit [12144] - f7d6ae1)

(based on commit [s1719] - 51661af)
[z2101] Refactor code around SMSG_PLAY_SPELL_VISUAL, drop dead code from Spell

(based on commit [12145] - c2440aa)

(based on commit [s1720] - cf3f01e)
Fixup script_command documentation. Thanks to crackm for pointing

(based on commit 6be541c)

Signed-off-by: Xfurry <xfurry@scriptdev2.com>

(based on commit 5eabc7e)

Signed-off-by: Xfurry <xfurry@scriptdev2.com>
Merge branch 'master' into testing