Merge pull request #79 from racklin/enhancement/strings

Added several strings Optimizers.
Added SubstrOptimizer and support negative start and length .

Signed-off-by: Rack Lin <racklin@gmail.com>
added TSRMLS_DC flag to zephir_fast_explode .

Signed-off-by: Rack Lin <racklin@gmail.com>
Merge pull request #80 from racklin/enhancement/substr

Added SubstrOptimizer.
Silent compilation of parser [ci skip]
Safer assumptions about substr parameters
Fixing assumptions about max supported long [ci skip]
Unit tests
Proper unit tests
Merge pull request #81 from Cinderella-Man/optimizers-fix

Optimizers fix
Improving assumptions about long parameters in optimizers, fixing missing TSRMLS_CC in zephir_feof, allowing null as empty string
Improving assumptions about offset parameter in StrposOptimizer.

Signed-off-by: Rack Lin <racklin@gmail.com>
Merge remote-tracking branch 'upstream/master'
Merge branch 'bugfix/subpos'