Support Short-circuit load (go-ini#261)

Co-authored-by: ᴜɴᴋɴᴡᴏɴ <u@gogs.io>

struct: Support reflect from struct with non-anonymous structure poin…

…ter (go-ini#259)

Co-authored-by: ᴜɴᴋɴᴡᴏɴ <u@gogs.io>

Co-authored-by: ᴜɴᴋɴᴡᴏɴ <u@gogs.io>

file: fix whitespaces are filtered in the SaveTo method (go-ini#260)

Allow alternative delimiter for child sections (go-ini#255)

ini: added option for ChildSectionDelimiter
file: added default for ChildSectionDelimiter (".") to maintain current behavior by default
section:
  - append ChildSectionDelimiter instead of "." when checking if each section name begins with prefix
  - use ChildSectionDelimiter instead of "." when checking for LastIndex of delimiter

Add options to control sections insensitive or keys insensitive respe…

…ctively (go-ini#253)

Co-authored-by: ᴜɴᴋɴᴡᴏɴ <u@gogs.io>

file: fix deleting the default section makes the next section inacces…

…sible (go-ini#256)

struct: correctly mapping non unique sections to slice field (go-ini#242

)

* bugfix: use the value from the correct section when using non unique sections in some special cases

* refactor wording and small fix

struct: ignore unexported fields when reflect (go-ini#239)

.travis: fix warnings

file: customize output delimiter (go-ini#226)

* customization output delimiter

* rename KeyValueDelimitersOutput to KeyValueDelimiterOnWrite

* add test for writing with KeyValueDelimiterOnWrite

* bugfix: use '=' as the default delimiter on write

Co-authored-by: Chaliy Roman <cerebrum.ch@gmail.com>