Table name case-sensitivity in to_sql
```python
import sqlite3
import pandas as pd

con = sqlite3.connect('testing.db')
cur = con.cursor()
cur.execute('CREATE TABLE test (A INT, B INT, C INT)')
con.commit()
df = pd.DataFrame({'A': 1, 'B': 2, 'C': 3}, index=[1,2,3])
df.to_sql('TEST', con, if_exists='append', index=False)
Traceback (most recent call last):
...
sqlite3.OperationalError: table "TEST" already exists

# This works
df.to_sql('test', con, if_exists='append', index=False)
```

I would think that table names should be case-insensitive. Even if they're not, the error that it's throwing does not describe the actual problem. 

#### Output of ``pd.show_versions()``

```
INSTALLED VERSIONS
------------------
commit: None
python: 3.6.4.final.0
python-bits: 64
OS: Windows
OS-release: 7
machine: AMD64
processor: Intel64 Family 6 Model 78 Stepping 3, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None
LOCALE: None.None

pandas: 0.22.0
pytest: 3.3.2
pip: 18.0
setuptools: 38.4.0
Cython: 0.27.3
numpy: 1.14.2
scipy: 1.0.0
pyarrow: 0.7.1
xarray: None
IPython: 6.2.1
sphinx: 1.6.6
patsy: 0.5.0
dateutil: 2.7.2
pytz: 2018.4
blosc: None
bottleneck: 1.2.1
tables: 3.4.2
numexpr: 2.6.4
feather: 0.4.0
matplotlib: 2.1.2
openpyxl: 2.4.10
xlrd: 1.1.0
xlwt: 1.3.0
xlsxwriter: 1.0.2
lxml: 4.1.1
bs4: 4.6.0
html5lib: 0.9999999
sqlalchemy: 1.2.1
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None
```
