[ENH] read_table(usecols = int | str) to produce squeezed Series
#### Problem description
This is a feature request for usecols to accept integer value and string.  If integer/string is provided, flag `squeeze` is to be turned on, thus producing a Series.

#### Rationale
+ consistency with `index_col` which accepts both integer/string and lists
+ shortcut

#### Expected Output

```python
# test
testfile = "pandas/tests/io/data/tips.csv"
df = pd.read_table(testfile, sep=",", usecols="tip")
assert isinstance(df, pd.Series)

df = pd.read_table(testfile, sep=",", usecols=2)
assert isinstance(df, pd.Series)

df = pd.read_table(testfile, sep=",", usecols=[2])
assert isinstance(df, pd.DataFrame)
```
#### Output of ``pd.show_versions()``

<details>
INSTALLED VERSIONS
------------------
commit: None
python: 3.3.2.final.0
python-bits: 64
OS: Linux
OS-release: 2.6.32-642.13.1.el6.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.19.0
nose: 1.3.0
pip: 8.1.2
setuptools: 20.9.0
Cython: 0.25.1
numpy: 1.11.2
scipy: 0.18.0
statsmodels: 0.6.1
xarray: None
IPython: 5.0.0.dev
sphinx: None
patsy: 0.4.1
dateutil: 2.5.3
pytz: 2016.6.1
blosc: None
bottleneck: None
tables: 3.3.1-dev0
numexpr: 2.6.1
matplotlib: 1.5.1
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: 4.4.1
html5lib: None
httplib2: 0.9.2
apiclient: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.8
boto: None
pandas_datareader: None
</details>
