implements nqp::sha1

Implements nqp::sha1 using the UTF-8 encoding of the input string.

Although a test is included (of an ASCII-compatible string), when a non-ASCII
input string is provided the test will fail.  For example, if the input
string is "Iñtërnâtiônàlizætiøn" the SHA-1 hash of the UTF-8 encoding should
be 4B9C5D2FA4C83F7561787EB4E5F7F06A2CD47425 (according to both the JVM and
nqp::sha1 on Parrot), but the test fails.  I'm not sure if this is an issue
with using non-ASCII characters in the test file or something deeper.
Merge pull request #4 from thecabinet/master

nqp::sha1
Remove completed task.
Merge branch 'master' of github.com:thecabinet/nqp-jvm-prep
Merge remote-tracking branch 'upstream/master'
implements nqp::exit
implements nqp::sleep
fixes documentation of nqp::sha1

Fixes documentation of nqp::sha1 (it's a serialization context opcode, not a
string opcode), and reorganizes its test code.