Ruby extension for GNU dbm (gdbm) -- a simple database engine for
storing key-value pairs on disk.

GNU dbm is a library for simple databases. A database is a file that
stores key-value pairs. Gdbm allows the user to store, retrieve, and
delete data by key. It furthermore allows a non-sorted traversal of
all key-value pairs. A gdbm database thus provides the same
functionality as a hash. As with objects of the Hash class, elements
can be accessed with []. Furthermore, GDBM mixes in the Enumerable
module, thus providing convenient methods such as #find, #collect,
#map, etc.

A process is allowed to open several different databases at the same
time. A process can open a database as a "reader" or a
"writer". Whereas a reader has only read-access to the database, a
writer has read- and write-access. A database can be accessed either
by any number of readers or by exactly one writer at the same time.
