Add an upper bound for repetition count. (But no syntax for it yet.)
Add e{n} e{,n} e{n,} and e{n,m} repetitions.

Fix #16
Update grammar.rs for prettyprint output due to use of blocks
Merge PR#20 Add e{n} e{,n} e{n,} and e{n,m} repetitions.

Conflicts:
	examples/tests.rs
	src/grammar.rs