add error checks for previously ignored error return values
Changes to conform with golint
Updated Constant mixed case issues to be in line with Go standards
Fixes #1
Fixes #2

Actually using MaxLineLength constant (whoops)
Fixed test to use appropriate attribute for HTML (not Html)
Merge branch 'master' of https://github.com/jessta/email into jessta-master

Conflicts:
	email.go
	email_test.go
Changes to use MaxLineLength again (looks like these got overwritten in the merge)
Changed Attach() to use a generic io.Reader
Attaching files is now done via AttachFile()
Updated README
Add leading space to comments
Safely concatenate addresses.

Formerly, appending directly to e.Bcc might have made unintended changes
to its underlying array.
Tighten Attach and AttachFile
Make Email.Attachments a slice
Return errors in Bytes()
Soup up base64Wrap, add test and benchmark.

It now uses less memory and is faster.

Previously:
Benchmark_base64Wrap    1000    2177418 ns/op    389576 B/op    2304 allocs/op

Now:
Benchmark_base64Wrap    2000    1282537 ns/op       145 B/op       1 allocs/op
Rewrite quotePrintEncode, add tests.

Problems included:
 - UTF-8 text was broken.  The input string was iterated over as runes,
   but any multi-byte character would have been broken.  E.g., the rune
   U+1f378 should be "=F0=9F=8D=B8".
 - Further, bytes less than 16 were also broken.  E.g.,
     fmt.Printf("=%X", '\r') == "=D"
 - Line breaks were not handled correctly; quoted-printable uses CRLF
   linebreaks.

Though the old approach wasn't entirely correct, it could have been
trivially fixed.  Thus, it's worth comparing benchmarks:

Old:
Benchmark_quotedPrintEncode    10000    125393 ns/op    9520 B/op    598 allocs/op

New:
Benchmark_quotedPrintEncode    500000      5325 ns/op      8 B/op      1 allocs/op