Change mock request to return empty json

Previously the mock returned an empty string as the request body. This
was converted to nil which breaks the (probably valid) assumption that
ErrorResponse#error makes when it calls @body["errorMessage"], that
@body will not be nil.
include error message when raising BadSyntax

Pass on error message from the ArangoDB server when raising BadSyntax
errors:

db.query.execute('FOR t IN TRAVERSE(imdb_vertices,
imdb_edges, "imdb_vertices/759", "outbound", {maxDepth: 2}) FILTER
t.vertex.genre == @foo RETURN t', bindVars: {"foo" => "Comedy" }).to_a

Ashikawa::Core::BadSyntax: 1540: usage of unknown function 'TRAVERSE()'
Merge pull request #110 from sleepycat/syntax_exception

Pass on server error messages when raising BadSyntax exceptions
Added Shield.io Badge for Code Coverage on CodeClimate
Merge pull request #106 from triAGENS/coverage-badge

Added Shield.io Badge for Code Coverage on CodeClimate
Update to RSpec 3.0.0
Use the master branch of all rspec gems
Merge pull request #112 from triAGENS/rspec-3.0.0

Use RSpec 3.0.0
Use bind_vars, not bindVars (thanks @railsbros-dirk)
Merge pull request #113 from triAGENS/bind_vars

Use bind_vars, not bindVars (thanks @railsbros-dirk)
Database#all_databases
Spec helper: Get a database object with random name

I don't really like this, but I have no idea on how to do that in a more
elegant way.
Acceptance Spec for creating a database
Connection#send_request_without_database_suffix and #database_name
Database#create
Yes, oh mighty Hound :dog:
For some reason Hound doesn't use the default for DotPosition

Setting the default by hand
A little bit of structure for the database_spec
Implemented Database#name
Implemented Database#drop