Improve the `isa` manual page:
 * Improve the rendering of the tool's options.
 * Note that "query" is the default mode of operation.
 * Allow specificiations to be specified as command line arguments.
 * Reword a paragraph for better clarity.

Ticket:	  #412

git-svn-id: https://elftoolchain.svn.sourceforge.net/svnroot/elftoolchain/trunk@2886 95820547-d848-0410-985e-9ae8fe0fa350
Update the usage message printed by `isa`.

Ticket:	#412

git-svn-id: https://elftoolchain.svn.sourceforge.net/svnroot/elftoolchain/trunk@2887 95820547-d848-0410-985e-9ae8fe0fa350
Add a `-h`/`--help` option to the `isa` utility.

Ticket:	#412

git-svn-id: https://elftoolchain.svn.sourceforge.net/svnroot/elftoolchain/trunk@2888 95820547-d848-0410-985e-9ae8fe0fa350
Changes to the `isa` utility:
 * Use the `-D`, `-E`, and `-Q` options, to specify the mode the
   utility is to operate in.
 * Expand the description of the command modes supported by the `isa`
   utility in the manual page.
 * Implement the rest of the command-line parser.
 * Add an EXAMPLE section to the manual page.

Ticket:	#412

git-svn-id: https://elftoolchain.svn.sourceforge.net/svnroot/elftoolchain/trunk@2889 95820547-d848-0410-985e-9ae8fe0fa350
Add a `check-specifications` target.

Ticket:	#412

git-svn-id: https://elftoolchain.svn.sourceforge.net/svnroot/elftoolchain/trunk@2890 95820547-d848-0410-985e-9ae8fe0fa350