added example for SI_ideal
Some cleanup, implement SI_ring()

Fixes #35
Use SI_RingOfSingobj directly instead of its SI_ring alias
Fix doubled IsCopyableObjSingular error msg
<Func Name="SingularLastOutput/Error" Arg=""/>
Move tests of type constructors into subdir tst/types/
deleted an ENTER
added example for SI_module
Implement SI_matrix constructor with string in GAP code
]]></Example> in new line
SI_ring( ) = SI_ring( 32003, "x,y,z" )
added string-version of SI_matrix to the example
Rename SI_Undef -> SingularUnbind, SI_ValueOfVar -> SingularValueOfVar
Rewrite SI_ideal & SI_ideal 'string' constructors in pure GAP
Remove old C++ code for creating SI_ideal/matrix/poly from strings
Remove obsolete naming conventions description
New namespace: SIC_ (for 'convenience')

First entries: factories for identity & zero mat
Rewrite SI_vector string constructor
documented SI_nrows, SI_ncols
SI_matrix( ideal ) in example