Harden 0.5.0 release checks

[prateekbhujel]

Summary

• harden COLUMNS/LINES parsing for getSize() environment fallback
• invalidate ModeToken objects after a successful restoreMode()
• add PHPT coverage and update 0.5.0 package/release notes

Tests

• git diff --check HEAD~2..HEAD
• php -l terminal.stub.php
• php -l examples/basic.php
• php -l examples/prompt.php
• php -l examples/doctor.php
• pear package-validate package.xml
• phpize && ./configure --enable-terminal && make
• make test REPORT_EXIT_STATUS=1 NO_INTERACTION=1 TEST_PHP_EXECUTABLE=/Applications/XAMPP/xamppfiles/bin/php
• php -n -d extension=/private/tmp/php-terminal-050-test.WTP1DB/modules/terminal.so examples/doctor.php