0032340: OCCT Documentation - highlight C++ code snippets

0032340: OCCT Documentation - highlight C++ code snippets

Added {.cpp} highlighting markers to the C++ code blocks in documentation;
Excessive tildes "~~~~~~~" in code block borders are reduced to required minimum of "~~~~" (4);
Removed obsolete space bars after code block borders;
TCL code blocks are now highlighted with {.php} markers;
Removed excessive {.cpp} highlighting markers appended to non-code blocks such as lists, reports and file content or structure examples;
Minor fixes for tests.md and draw_test_harness.md (whitespace removal and structural fix for "Where:" in code examples);
Minimum HDD space for OCCT updated in introduction.md.