(Work-in-progress) Add an implementation of a string table handling
API.

Ticket: #367


git-svn-id: https://elftoolchain.svn.sourceforge.net/svnroot/elftoolchain/trunk@2859 95820547-d848-0410-985e-9ae8fe0fa350
Update the `libelftc` test suite:
 * Track the changes to the string table APIs in changeset [2858].
 * Add additional tests for these APIs.

Ticket: #361

git-svn-id: https://elftoolchain.svn.sourceforge.net/svnroot/elftoolchain/trunk@2860 95820547-d848-0410-985e-9ae8fe0fa350
Add the tests for the string table APIs to the definition of the
`libelftc` test suite.

Ticket:	#361

git-svn-id: https://elftoolchain.svn.sourceforge.net/svnroot/elftoolchain/trunk@2861 95820547-d848-0410-985e-9ae8fe0fa350