Support omission of variable in dotimes and dolist
Merge pull request #4 from rui314/master

Parallelize sub-makes in ext/ to improve clean build speed
Support letrec*
Should clear whole content, not pointer size
Merge pull request #5 from k-tsj/fix-incorrect-zeroing

Fix incorrect zeroing in rfc.sha
Expose letrec* to r7rs
Doc for letrec*
Fix a bug that assumes size_t can be negative.