Latin1 string encoding

[jasongin]

N-API currently supports UTF-8 and UTF-16 string encoding. V8 additionally supports latin1 string encoding, called "OneByte" strings in the V8 APIs, and it is widely used.

Proposed additional APIs:

• napi_create_string_latin1
• napi_get_value_string_latin1_length
• napi_get_value_string_latin1

[sampsongao]

#192

[jasongin]

Closing since this was done and merged into node.