Expand spec helper method asset_path

It receives path after asset directory
Moved Adaptor::SQLite3#getimage to Adaptor
New spec helper function read_logo
Convert logo file from xpm to png
New spec for DB::Adaptor#getimage
Reimplement Adaptor#getimage using PixbufLoader
Additional spec for Adaptor#getimage

Should return Gtk::Image even if truncated data is fed
Reimplement Adaptor#getimage

Resume when truncated data is fed
Cosmetics
Merge commit 'v0.1.7'
Additional spec for Adaptor#getimage
Use simplecov instead of rcov
Load test group bundle
Use simplecov or rcov accordingly to RUBY_VERSION
Filter out spec/* files from SimpleCov output
Merge branch 'jeweler'
Eliminate unnecessary flatten
New spec for Rimv::Keyval
Remove logo.xpm
Version bump to 0.1.8