Improve Context construction and representation:

Improve Context construction and representation:

* Rename "trap_enablers" to just "traps".
* Simplify names of "settraps" and "setflags" to just "traps" and "flags".
* Show "capitals" in the context representation
* Simplify the Context constructor to match its repr form so that only
  the set flags and traps need to be listed.
* Representation can now be run through eval().

Improve the error message when the Decimal constructor is given a float.

The test suite no longer needs a duplicate reset_flags method.