Implement 'neoterm_bracketed_paste' option.

[echasnovski]

This PR is a suggestion for #295 solution. It introduces g:neoterm_bracketed_paste setting: value 0 (default) disables bracketed paste (which is exactly the current situation), value 1 enables it.

Here are (many) examples of how this setting works with neoterm_repl_r equal to "radian" and "r" and neoterm_repl_python equal to "ipython" and "python". In every one of them I execute TREPLSendFile, TREPLSendSelection, and TREPLSendLine:

Examples

radian

Bracketed paste enabled (everything works):
Bracketed paste disabled (only sending single line works with default radian settings):

R

Bracketed paste enabled (everything works):
Bracketed paste disabled (everything works; notice that every line is executed sequentially because '+' is present at its beginning):

ipython

Bracketed paste enabled (everything works):
Bracketed paste disabled (only sending single line works; notice in terminal buffer extra indentation inside function body):

python

Bracketed paste enabled (only sending single line works because Python gives SyntaxError: multiple statements found while compiling a single statement):
Bracketed paste disabled (everything works):

To sum up, when this setting is on, Neoterm can send multiline code to radian, R, and ipython, but not plain Python (because it can't compile multiple statements).

@kassio, I would really like this PR to be merged, as this seems to be a very crucial addition. If you give green light here (code is correct, names are appropriate), I'll update 'CHANDELOG.md' and 'neoterm.txt' (please, show the place where this setting should go and if there is any extra information you would like me to put there). Thanks.

[strboul]

Great @echasnovski you've picked this up. I tried your version (steps explained here) on mac OS Mojave and it seems to work well with radian. There's a disturbance that the echoed text after :TREPLSend* displays the escape sequences. It'd be nice if there's a way to remove them.

[echasnovski]

@strboul, thanks for additional testing.

Yes, those echoing escape characters are somewhat disturbing, but I currently don't have any idea of how to remove them. I am even not really sure about the purpose of this echoing (if this is "a bug or a feature"), as it is also present in main version.

[echasnovski]

Thanks, @kassio. How about updating changelog and documentation?

[kassio]

@echasnovski, ooopsss.. Can you add another pull request, please?

[echasnovski]

@echasnovski, ooopsss.. Can you add another pull request, please?

@kassio, no problem. Created #297.