Added block detection and execute whole block

[Ladvien]

This PR provides functionality which should truly close #27.

If a partial block is selected, for example,

myFunction <- function() {
   foo$Bar <- "FooBar"
...

It should parse one line at a time until it finds the termination of the block.

It should also handle whole and half blocks.

myFunction <- function() {
   foo$Bar <- "FooBar"
}

myFunctionTwo <- function() {
   foo$Bar <- "FooBar"

And bidirectional block checking:

foo$Bar <- "FooBar"
}

myFunctionTwo <- function() {
   foo$Bar <- "FooBar"
}

Once I've received some feed back, I'll expand this to include looking at multiline functions. For example,

myFunction(x = 2,
                     y = 3)

[Ikuyadeu]

@Ladvien Thank you for good PR!
I'll review this in this weekend.

[Ikuyadeu]

OK, I checked.
Thank you good PR @Ladvien !