fix Position checking

fixes #274
Merge pull request #275 from Garonenur/dw

fix Position checking
unsigned long -> GtUword
Merge pull request #276 from gordon/uword

unsigned long -> GtUword
Closes #278.
make hashmap methods optional to use

Closes #277.
remove unused hashmap declaration
remove unused functions
Merge pull request #280 from satta/unused_hashmap

Unused functions
Merge pull request #279 from standage/strand

Closes #278.
add -retainids to `gt merge'
accept and ignore empty input GFF3s in tidy modes
gtruby: fix FeatureNode.set_source
properly initialize string buffers

Closes #282.
warn when weird characters appear in argv

Closes #241.
Update README.md

add link to gitter chatroom
closes #230
Merge pull request #283 from satta/sanger

Some bugfixes and minor feature additions
Merge pull request #284 from Garonenur/gitter

Update README.md