Fix 64-bit compatibility compiler warnings

Fix compiler warnings in case of sizeof(unsigned)!=sizeof(size_t)
 * HASH_FIND_STR is tested
 * HASH_REPLACE_STR is not tested
 * no (additional) cast required for HASH_ADD_STR since already done in HASH_ADD_KEYPTR
Fix scope of some variables

as reported by Cppcheck
fix issue reported by LikwidCirkel
Merge pull request #39 from tbeu/fix-scope

Fix scope of some variables
Merge branch 'master' of github.com:troydhanson/uthash
doc tweaks
fix
Merge pull request #35 from tbeu/patch-1

Fix 64-bit compatibility compiler warnings
Add utstring_truncate, analogous to man (2) truncate