FMSLogo Code

Formally thank Peter De Watcher for opening a bug report on gcc
that caused logomath.cpp to fail to compile when optimizations
are enabled. See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71020

Fix a class of warnings that is emitted by recent versions of g++:
warning: invalid suffix on literal; C++11 requires a space between literal and string macro [-Wliteral-suffix]

Fix a macro redefinition warning when compiling on Fedora Core 25.

Fix Bug #485; Remove the synopsis for EDIT taking zero inputs. There is some behavior for this in UCBLogo (re-opening the same file as used in a previous EDIT call), but since FMSLogo also deletes the temp file after closing, this behavior doesn't make sense in FMSLogo. Instead of trying to add it, I decided to document the existing behavior.

Fix Bug #485; Remove an extraneous double-quote for the input to TO in the example code for the EDIT variants. This problem dates back to MSWLogo's manual.

Use the present tense, not the future tense.

Port MESSAGEBOX to be implementing using wxWidgets instead of win32-specific functions so that it's avaiable on GNU/Linux builds of FMSLogo.

Fix bug #484; BYE now immediately exits when run at the top-level of a file that is loaded from the command-line.

The heart of the fix is to make all primitives return an Unbound value when exiting to avoid the "you don't say what to do with" errors. The rest of the changes udpate all parts that of the code that evaluate Logo code to do so within a start_execution() and stop_execution() so that a "close" event can be sent if the application is exiting.

Simplify the shutdown logic. Also fix a bug that caused the debug screensaver to have assert failure (the size of the wxTempDC needed to be set)

Correct the names of global variables and a function in a comment (this was a copy&paste legacy from the OWL implementation).