WIP: Fix import breakage due to JuliaLang/julia#11333

[jrevels]

This PR is an attempt to fix the import breakage discussed in #19. Specifically, it causes import/using statements to be parsed in accordance to JuliaLang/julia#11333, i.e. a newline or ; is no longer required to terminate the statement.

All added tests pass locally, and no additional failures have occurred, except for the test for parsing "begin using A end". However, I can't seem reproduce this failure outside the scope of the specific test:

# Called from ~/.julia/JuliaParser/test, on the fix-import branch.
# There were 21 tests failing on master already, so below 
# I'll just skip to the failure that this PR currently adds.
julia> include("runtests.jl") 
⋮
test import / using / importall expressions
  Failure   :: (line:442) :: Expected: begin  # none, line 1:
    using A
end => begin  # /Users/jarrettrevels/.julia/JuliaParser/test/parser.jl, line 1:
    using A
end
    Parser.parse(ex) --> Base.parse(ex)
Out of 24 total facts:
  Verified: 23
  Failed:   1
⋮
ERROR: LoadError: FactCheck finished with 22 non-successful tests. 
 in error at ./error.jl:21
 in exitstatus at /Users/jarrettrevels/.julia/FactCheck/src/FactCheck.jl:500
 in include at ./boot.jl:254
 in include_from_node1 at ./loading.jl:197
while loading /Users/jarrettrevels/.julia/JuliaParser/test/runtests.jl, in expression starting on line 8

julia> ex = """begin using A end""" # the erroring statement
"begin using A end"

julia> Parser.parse(ex) == Base.parse(ex) # somehow works?
true

[jakebolewski]

Thanks @jrevels, I'll have a look at the issue you mentioned.