abi string type, fixes #216, #218, #219

[debris]

This pr brings back string type for solidity.

@ethers @chriseth @frozeman can you review tests?

[coveralls]

Coverage increased (+0.05%) to 94.53% when pulling fa3239f on strings into 7753724 on develop.

[coveralls]

Coverage increased (+0.05%) to 94.53% when pulling 73cc711 on strings into 448dd30 on develop.

[chriseth]

Would be great to have tests for actual unicode / utf8.

[coveralls]

Coverage increased (+0.05%) to 94.53% when pulling 189484f on strings into 448dd30 on develop.

[coveralls]

Coverage increased (+0.06%) to 94.54% when pulling 7b730b1 on strings into 448dd30 on develop.

[chriseth]

Would be great to have tests for en- and decoding the following:

• correctly encoded utf-8 string containing non-ascii characters
• incorrectly encoded utf-8 string terminating prematurely (e.g. "\xc3")
• utf-8 strings containing internal zeros (e.g. "\xc3\xa4\x00\x00\xc3\xa4")

[LefterisJP]

May I suggest this UTF8 encoding/decoding stress testing collection? I use it in one of my projects.

[frozeman]

@debris please merge this PR asp, as solidity has now string and array support and the wallet dapp depends on that and its now not aligned with solidity.

Additionally we should give a note to the community that auto conversion of bytes has been removed.

[frozeman]

@debris URF8 encoding seems to work fine, but decoding seems broken:

> "\xc3\xa4\x00\x00\xc3\xa4"
"ä��ä"

> web3.fromAscii("\xc3\xa4\x00\x00\xc3\xa4")
"0xc3a40000c3a4"

> web3.toAscii('0xc3a40000c3a4')
"ä"

[frozeman]

@debris ok changed, could please also take a look and as well at the encoding issue i mentioned above above:

> "\xc3\xa4\x00\x00\xc3\xa4"
"ää"

> web3.fromAscii("\xc3\xa4\x00\x00\xc3\xa4")
"0xc3a40000c3a4"

> web3.toAscii('0xc3a40000c3a4')
"ä"

[debris]

@debris ok changed, could please also take a look and as well at the encoding issue i mentioned above above:

"\xc3\xa4\x00\x00\xc3\xa4"
"ää"

web3.fromAscii("\xc3\xa4\x00\x00\xc3\xa4")
"0xc3a40000c3a4"

web3.toAscii('0xc3a40000c3a4')
"ä"

decoding solidity strings does not use web3.toAscii internally. I added few tests in 93c8006 . I will fix it in another pr.

Let's merge!

[frozeman]

Ok but then lets actually rename toAscii to toString, as its no converting to ascii but latin something..