Upgrade to Solidity v0.5.0

[fubuloubu]

• Style changes
• Added memory everywhere to bytes and strings
• target.call(data) now returns a tuple

[GNSPS]

I just changed the target branch to develop to follow the same flow for all the previous versioned releases (merged the file in the latest commit) and updated the README with a note about compiler support.
Also made the change to have the CI install Truffle v5 and use solc v0.5.1 but tests ran locally seem to be failing for me for some reason. Do they pass if you run $ truffle test, @fubuloubu ?

[GNSPS]

Ok, test are passing now on my machine. Overall ditching the ThrowProxy was probably a good v0.5.x improvement either way, so... 😄

Let me know if you're ok with me merging the request as is @fubuloubu .

[fubuloubu]

Looking good for me. The tests complain about the following unused variables:

Compilation warnings encountered:                                                                                                        
                                                                                                                                         
/home/bryant/Documents/solidity-bytes-utils/test/TestBytesLib1.sol:262:9: Warning: Unused local variable.                                
        bytes memory postBytes4 = hex"f00dfeed";                                                                                         
        ^---------------------^                                                                                                          
,/home/bryant/Documents/solidity-bytes-utils/test/TestBytesLib1.sol:263:9: Warning: Unused local variable.                               
        bytes memory postBytes31 = hex"f00d000000000000000000000000000000000000000000000000000000feed";                                  
        ^----------------------^                                                                                                         
,/home/bryant/Documents/solidity-bytes-utils/test/TestBytesLib1.sol:264:9: Warning: Unused local variable.                               
        bytes memory postBytes32 = hex"f00d00000000000000000000000000000000000000000000000000000000feed";                                
        ^----------------------^    

It looks like in your tests, this doesn't match up with what I think is intended (I'd expect each preBytes to do something with it's corresponding postBytes), but that's outside the scope of this PR.