fix embedded struct copy

[fix] #78 Note that a copy was made after successful copy

fix #92

append destslice size only if dest size smaller than src

fix #92

fix bug introduced by #93

try copier while failed to set slice element with struct type

Copy different field name from tag flag

Copy un-exported struct fields in DeepCopy

Add support to copy from a nil slice pointer to a slice field when DeepCopy is enabled

added converter option for type conversions

fix bug from issue 117 that 'Copy map with slice-type value panic'

style: simplify shouldIgnore