Log Message:
Update ruby-roo to 2.5.1.

## [2.5.1] 2016-08-26
### Fixed
- Fixed NameError. [337](https://github.com/roo-rb/roo/pull/337)

## [2.5.0] 2016-08-21
### Fixed
- Remove tempdirs via finalizers on garbage collection. This cleans them up in \ 
all known cases, rather than just when the #close method is called. The #close \ 
method can be used to cleanup early. \ 
[329](https://github.com/roo-rb/roo/pull/329)
- Fixed README.md typo [318](https://github.com/roo-rb/roo/pull/318)
- Parse sheets in ODS files once to improve performance \ 
[320](https://github.com/roo-rb/roo/pull/320)
- Fix some Cell conversion issues [324](https://github.com/roo-rb/roo/pull/324) \ 
and [331](https://github.com/roo-rb/roo/pull/331)
- Improved memory performance [332](https://github.com/roo-rb/roo/pull/332)
- Added `no_hyperlinks` option to improve streamig performance \ 
[319](https://github.com/roo-rb/roo/pull/319) and \ 
[333](https://github.com/roo-rb/roo/pull/333)

### Deprecations
- Roo::Base::TEMP_PREFIX should be accessed via Roo::TEMP_PREFIX
- The private Roo::Base#make_tempdir is now available at the class level in
  classes that use tempdirs, added via Roo::Tempdir
=======
### Added
- Discard hiperlinks lookups to allow streaming parsing without loading whole files

## [2.4.0] 2016-05-14
### Fixed
- Fixed opening spreadsheets with charts \ 
[315](https://github.com/roo-rb/roo/pull/315)
- Fixed memory issues for Roo::Utils.number_to_letter \ 
[308](https://github.com/roo-rb/roo/pull/308)
- Fixed Roo::Excelx::Cell::Number to recognize floating point numbers \ 
[306](https://github.com/roo-rb/roo/pull/306)
- Fixed version number in Readme.md [304](https://github.com/roo-rb/roo/pull/304)

### Added
- Added initial support for HTML formatting \ 
[278](https://github.com/roo-rb/roo/pull/278)