doc: add nodejs.org.au to community listing
doc: add nodejs.geek.nz to the community page
doc: clarify fs.read() offset argument
string_bytes: add StringBytes::IsValidString()

Performs a quick, non-exhaustive check on the input string to see if
it's compatible with the specified string encoding.

Curently it only checks that hex strings have a length that is a
multiple of two.
crypto: fix assert() on malformed hex input

Use the StringBytes::IsValidString() function introduced in commit
dce26cc to ensure that the input string meets the expectations of the
other StringBytes functions before processing it further.

Fixes the following assertion:

    Assertion failed: (str->Length() % 2 == 0 && "invalid hex string
    length"), function StorageSize, file ../../src/string_bytes.cc,
    line 301.

Fixes #5725.
docs: Warning about consuming response
http: improve chunked res.write(buf) performance

Avoid a costly buffer-to-string operation. Instead, allocate a new
buffer, copy the chunk header and data into it and send that.

The speed difference is negligible on small payloads but it really
shines with larger (10+ kB) chunks. benchmark/http/end-vs-write-end
with 64 kB chunks gives 45-50% higher throughput. With 1 MB chunks,
the difference is a staggering 590%.

Of course, YMMV will vary with real workloads and networks but this
commit should have a positive impact on CPU and memory consumption.

Big kudos to Wyatt Preul (@wpreul) for reporting the issue and providing
the initial patch.

Fixes #5941 and #5944.